Search

Although intraspecific trait variation is increasingly recognized as affecting ecosystem processes, few studies have examined the ecological significance of among-population variation in behavioral traits in natural ecosystems. In freshwater habitats, crayfish are consumers that can influence ecosystem structure (e.g., macroinvertebrate communities) and function (e.g., leaf litter breakdown). To test whether crayfish behavioral traits (activity, boldness, and foraging voracity) are major contributors of leaf litter breakdown rates in the field, we collected rusty crayfish (Faxonius rusticus) from eight streams across the midwestern USA and measured behaviors using laboratory assays. At the same streams, we measured breakdown rates of leaf packs that were accessible or inaccessible to crayfish. Our results provide evidence that among-population variation in crayfish boldness and foraging voracity was a strong predictor of leaf litter breakdown rates, even after accounting for commonly appreciated environmental drivers (water temperature and human land use). Our results suggest that less bold rusty populations (i.e., emerged from shelter more slowly) had greater direct impacts on leaf litter breakdown than bold populations (P = 0.001, r2 = 0.85), potentially because leaf packs can be both a shelter and food resource to crayfish. Additionally, we found that foraging voracity was negatively related to breakdown rates in leaf packs that were inaccessible to crayfish (P = 0.025, r2 = 0.60), potentially due to a trophic cascade from crayfish preying on other invertebrates that consume leaf litter. Overall, our results add to the growing evidence that trait variation in animals may be important for understanding freshwater ecosystem functioning. [ABSTRACT FROM AUTHOR]

Urban stormwater ponds (SWPs) are engineered ecosystems designed to prevent flooding and protect downstream ecosystems by retaining nutrients associated with stormwater runoff, including nitrogen (N). Despite these expectations, multiple studies have found that SWPs have low N removal efficiencies and can be sources of N to downstream ecosystems. To understand mechanisms controlling the fate of N in SWPs, we quantified dinitrogen (N2) gas saturation to characterize net N2 exchange as either net denitrification or net N-fixation. We assessed temporal and spatial patterns of N2 dynamics in fifteen SWPs and six naturally occurring ponds in undisturbed watersheds (Florida, USA) by sampling in two seasons (dry and wet) and from multiple depths of the water column. Samples from SWPs were equally likely to exhibit N2 supersaturation (net denitrification; 50%) or undersaturation (net N-fixation; 50%). In contrast, the majority (82%) of samples from natural ponds were supersaturated with N2, indicating net denitrification. The mean SWP air–water N2 flux was − 1.7 μg N2-N m−2 h−1 (range − 500 to 433 μg N2-N m−2 h−1), which was lower than clear (40 μg N2-N m−2 h−1; range − 68 to 74 μg N2-N m−2 h−1) and humic (202 μg N2-N m−2 h−1; range 41 to 407 μg N2-N m−2 h−1) natural ponds despite considerably higher variation in SWPs. These results indicate that SWPs may have low N removal efficiencies in part due to N-fixation adding new N to the system. Overall, this study shows that SWPs are less effective than natural ponds at removing reactive N from the environment, potentially impacting downstream water quality. [ABSTRACT FROM AUTHOR]

Salinization and eutrophication are nearly ubiquitous in watersheds with human activity. Despite the known impacts of the freshwater salinization syndrome (FSS) to organisms, we demonstrate a pronounced knowledge gap on how FSS alters wetland biogeochemistry. Most experiments assessing FSS and biogeochemistry pertain to coastal saltwater intrusion. The few inland wetland studies mostly add salt as sodium chloride. Sodium chloride alone does not reflect the ionic composition of inland salinization, which derives from heterogeneous sources, producing spatially and temporally variable ionic mixtures. We develop mechanistic hypotheses for how elevated ionic strength and changing ionic composition alter urban wetland sediment biogeochemistry, with the prediction that FSS diminishes nutrient removal capacity via a suite of related direct and indirect processes. We propose that future efforts specifically investigate inland urban wetlands, a category of wetland heavily relied on for its biogeochemical processing ability that is likely to be among the most impacted by salinization. [ABSTRACT FROM AUTHOR]

Despite the assumption that residential fertilizer ordinances improve regional water quality, their impacts across space and time largely remain unknown. Here, we analyze changes in water quality of lakes throughout the State of Florida from 1987 to 2018, comparing trends in water quality parameters before and after implementation of county‐wide fertilizer ordinances. We used a large dataset of publicly collected water quality data and linear mixed models to analyze ordinance impacts on total nitrogen, total phosphorus, chlorophyll a, and Secchi depth across 160 lakes throughout Florida. We further analyze water quality impacts relative to the type of ordinance (winter fertilizer ban, summer ban, nonseasonal ban, no ban). We found fertilizer ordinances favorably impacted lacustrine water quality, and winter (dry season) fertilizer bans had the greatest effect across all water quality metrics. Results of this study can be used to support the effectiveness of fertilizer ordinances across humid tropical and subtropical climate regions. [ABSTRACT FROM AUTHOR]

Stormwater wet detention ponds (hereafter "detention ponds") are implemented to mitigate impacts of urban stormwater runoff on downstream waterbodies. We evaluated the effectiveness of detention ponds in providing this protection by quantifying hydrological, chemical, and biological responses in urban depressional wetlands with and without detention ponds draining into them and comparing these responses to non-urban reference depressional wetlands. We predicted if detention ponds protect waterbodies, then the hydrology, water and soil chemistry, and plant communities of urban depressional wetlands receiving detention pond drainage should be more similar to non-urban depressional wetlands than urban depressional wetlands not receiving detention pond drainage. We found wetlands receiving detention pond drainage had post-storm water level recession rates that were slower than wetlands not receiving detention pond drainage, but faster than non-urban wetlands. We also found wetlands with and without detention ponds draining into them (i.e., urban wetlands) to be more similar to each other regarding water and soil chemistry and vegetation than to non-urban wetlands. Compared to non-urban wetlands, both urban wetland types had elevated pH, inorganic nitrogen, and total phosphorus in their soils and waters, and greater coverage and species richness of disturbance-adapted native and nonnative plant species of lower conservation value. Differences in plant communities were related to changes in hydrology and water and soil chemistry, suggesting detention ponds need to better mitigate the effects of urbanization on these factors. Our findings reveal the need to improve detention pond efficiency and/or identify alternative strategies for protecting waterbodies from the effects of urbanization. [ABSTRACT FROM AUTHOR]

Lakes process both terrestrial and aquatic organic matter, and the relative contribution from each source is often measured via ecosystem metabolism and terrestrial resource use in the food web (i.e., consumer allochthony). Yet, ecosystem metabolism and consumer allochthony are rarely considered together, despite possible interactions and potential for them to respond to the same lake characteristics. In this study, we compiled global datasets of lake gross primary production (GPP), ecosystem respiration (ER), and zooplankton allochthony to compare the strength and shape of relationships with physicochemical characteristics across a broad set of lakes. GPP was positively related to total phosphorus (TP) in lakes with intermediate TP concentrations (11–75 μg L−1) and was highest in lakes with intermediate dissolved organic carbon (DOC) concentrations. While ER and GPP were strongly positively correlated, decoupling occurred at high DOC concentrations. Lastly, allochthony had a unimodal relationship with TP and related variably to DOC. By integrating metabolism and allochthony, we identified similar change points in GPP and zooplankton allochthony at intermediate DOC (4.5–10 mg L−1) and TP (8–20 μg L−1) concentrations, indicating that allochthony and GPP may be coupled and inversely related. The ratio of DOC:nutrients also helped to identify conditions where lake organic matter processing responded more to autochthonous or allochthonous organic matter sources. As lakes globally face eutrophication and browning, predicting how lake organic matter processing will respond requires an updated paradigm that incorporates nonlinear dynamics and interactions. [ABSTRACT FROM AUTHOR]

Nitrogen (N) removal from stormwater runoff prior to its export to sensitive downstream water bodies is a common goal for urban stormwater ponds (SWPs). Denitrification removes nitrate (NO3−) from stormwater runoff by conversion to di-nitrogen gas (N2), permanently removing reactive N from the ecosystem. Typically, N removal in SWPs is quantified via mass balance approaches, but the internal biogeochemical mechanisms driving N dynamics in these engineered ecosystems are unclear. In this study, we quantified gaseous and dissolved inorganic N fluxes and sediment oxygen demand from sediment cores collected at residential SWPs ranging from 10 to 30 years old in two subtropical cities during the dry and wet seasons. To better understand biogeochemical process rates and drivers within SWP sediments, we exposed sediments to both ambient and elevated (to simulate stormwater runoff) water column nitrate concentrations. Under ambient concentrations, SWP sediments could be either net sources (via N-fixation) or sinks (via denitrification) for N, and net N2 flux was not significantly affected by background nitrate concentrations, sediment oxygen demand, or age. However, SWP sediments shifted to net denitrification under elevated nitrate conditions. Denitrification (positive net N2 flux) increased with SWP age, microbial activity, and net nitrate uptake (p < 0.05 for each). These results suggest that while denitrification is N limited under ambient conditions, SWPs have the capacity to rapidly process acute nitrate loading events and remove N from the water column via denitrification. [ABSTRACT FROM AUTHOR]

Wastewater reclamation facilities are known sources of emerging contaminants associated with human health and sanitation. This study evaluated the contribution of trace organic contaminants to a previously unmonitored river by water resource reclamation facilities. Six sampling events were conducted on the Reedy River in South Carolina. Sampling locations included sites upstream and downstream of two WRRFs located on the river to examine potential contributions under drought conditions where WRRF effluents comprise a large proportion of total stream flow. Five target analytes were monitored including atrazine, carbamazepine, 17β-estradiol, perfluorooctanoic acid, and sulfamethoxazole. On a mass basis, the WRRFs contributed additional loadings of carbamazepine ranging from 5.4 g/d to 7.2 g/d (mean: 6.3 ± 0.4 g/d), PFOA ranging from 8.6 to 31.9 g/d (mean: 20.0 ± 4.9), and sulfamethoxazole ranging from 49.4 g/d to 75.1 g/d (mean: 62.1 ± 4.8). 17β-estradiol was detected once and atrazine was not detected. [ABSTRACT FROM AUTHOR]

Designed ecosystems (e.g., gardens or engineered ponds) are increasingly common components of urban landscapes and contribute valuable ecosystem services. However, management of designed ecosystems is typically vegetation-centric and often does not consider associated fauna. Urban ponds typify this relationship as their vegetation is managed to improve ecosystem services, such as aesthetics and stormwater runoff mitigation, but it is unclear how pond management affects associated organisms. Here, we used urban stormwater ponds as a study system to determine how vegetation management related to benthic macroinvertebrate communities in these systems. We compared macroinvertebrates across a range of actively managed to unmanaged stormwater ponds and differentiated direct relationships with vegetation structure from indirect relationships of vegetation modulating pond chemistry. Pond vegetation and chemistry had little influence on macroinvertebrate abundance or diversity but did explain substantial variability in community composition (34%). Actively managed stormwater ponds with simpler vegetation structure were dominated by Amphipoda (scuds) and Diptera (primarily midges), unmanaged ponds with more complex structure were dominated by Oligochaeta (worms), and ponds with intermediate structure were dominated by a variety of macroinvertebrates. These community associations with vegetation management primarily occurred indirectly via changes in pond chemistry, such as unmanaged ponds with higher tree and shrub cover harboring macroinvertebrates characteristic of low oxygen environments. Additionally, variation in management maximized community differences because different macroinvertebrate orders dominated at different management intensities. Variability in the management intensity of plant communities in stormwater ponds may therefore be a feasible strategy to enhance regional benthic macroinvertebrate biodiversity in urban landscapes. [ABSTRACT FROM AUTHOR]

Pharmaceuticals are ubiquitous in aquatic environments, yet little is known regarding their impacts on ecological processes. Selective serotonin reuptake inhibitors (SSRIs) are frequently prescribed human antidepressants and have been shown to alter crayfish behavior. These behavioral alterations are particularly relevant as crayfish play a central role in freshwater ecosystems and often reach high biomass in anthropogenically influenced environments commonly exposed to pharmaceutical contamination. Using a 14‐d artificial stream experiment, we exposed spinycheek crayfish (Faxonius limosus) to citalopram, a common SSRI, at an environmentally realistic concentration (0.5 µg/L). We used a Y‐shaped flume to quantify the effects of SSRI exposure on crayfish behavior and food/conspecific preference. We also tested the interacting effects of citalopram and crayfish on habitat‐specific and whole‐stream ecosystem functions and biomass. Crayfish exposed to SSRIs exhibited increased boldness (time to emerge from shelters; P < 0.05) and spent more time orienting to food resources than nonexposed crayfish. Crayfish increased water column chlorophyll a (P < 0.01) and benthic organic matter (P = 0.03). Furthermore, crayfish potentially increased water column respiration (P = 0.09) and potentially decreased nitrate uptake (P = 0.05). SSRI exposure exhibited a potential effect of decreasing benthic chlorophyll a (P = 0.07), but there were no significant CRAY+SSRI interactions. Neither crayfish nor SSRI treatments affected whole‐stream metabolism. These results suggest that citalopram has the potential to affect algal biomass but did not affect ecosystem functioning. However, alterations to crayfish behavior driven by SSRI exposure could lead to subsequent ecosystem‐level effects as crayfish did affect various response metrics. We were unable to detect the effects of altered crayfish behavior at the ecosystem scale during our study, likely due to the short time frame (2 weeks) of our experiment. Further work is needed to quantify longer‐term ecosystem consequences of sublethal effects of pharmaceuticals, but these results show that ecological responses to pharmaceuticals should consider the entire ecosystem. [ABSTRACT FROM AUTHOR]

Urbanization increases stormwater runoff into streams, resulting in channel erosion, and increases in sediment and nutrient delivery to receiving water bodies. Stream restoration is widely used as a Best Management Practice to stabilize banks and reduce sediment and nutrient loads. While most instream nutrient retention measurements are often limited to low flow conditions, most of the nutrient load is mobilized at high stream flows in urban settings. We, therefore, use a process‐based stream ecosystem model in conjunction with measurements at low flows and focus on estimation of stream nitrogen retention over the full streamflow distribution. The model provides a theoretical framework to evaluate the geomorphic, hydrologic, and ecological factors that are manipulated by stream restoration, and drive nitrogen retention. We set a model for a pool‐riffle sequence restored stream (190 m) in Baltimore County, Maryland and calibrated the model to the in situ measured primary production (Nash–Sutcliffe model efficiency coefficient [NSE] NSE = 0.89), respiration (NSE = 0.74), and nitrate uptake lengths (R2 = 0.88). At the daily scale, simulations showed low nitrogen retention during high flows due to high transport rates, mobilization of stored hyporheic nitrogen, and scouring of periphyton biomass. This result underscores the need to reduce contributing watershed runoff flashiness to promote aquatic nutrient cycling and retention. At monthly and yearly time scale, model predicted a higher percent reduction in summer than in winter and estimated 5.7%–9.5% of annual nitrate reductions. While the model was tested in a pool‐riffle sequence restoration design, the approach can be adapted to evaluate a range of channel restoration design characteristics, and the effects of upland watershed restoration to mitigate stormwater loading through both restored and unrestored streams. Research Impact Statement: This study provides a coupled data and process modeling‐based framework to investigate stream ecosystem over a full flow regime, and to evaluate the benefits of stream restoration to increase nutrient retention. [ABSTRACT FROM AUTHOR]

Research has inadequately examined factors that support residential yard care practices that influence water quality to date. This study evaluated factors that predict yard fertilizer best practices in the state of Florida, USA by pairing the Theory of Planned Behavior and Diffusion of Innovations along with contextual factors including age, population density, and living in a homeowners' association. Data were collected from 1,197 Florida residents using an electronic researcher-developed survey instrument. Alone, all TPB variables (attitude, perceived behavioral control, subjective norms) predicted behavioral intent. When Diffusion of Innovation characteristics were added, compatibility predicted intent along with the TPB variables. When contextual variables were added to the final model, the same variables remained significant and age (younger), living in an HOA, and not living in a metro with less than 250,000 people predicted behavioral intent. Findings offer new insights into residential yard fertilizer behaviors informed by integrating the two theories. [ABSTRACT FROM AUTHOR]

Lotic and lentic ecosystems are traditionally viewed as dominated by either benthic or water column processes. However, mid-sized rivers represent a transition zone where both benthic and water column processes may both contribute substantially to ecosystem dynamics. Ecosystem processes such as gross primary production (GPP), ecosystem respiration (ER), or nutrient uptake, and the relative contribution of the water column to these processes at the reach scale, are poorly understood in non-wadeable, mid-sized rivers. To clarify the role of the water column at the reach-scale, and to quantify controls on water column processes, we measured GPP, ER, and uptake of nitrate (NO3−), ammonium (NH4+), and soluble reactive phosphorus (SRP) in the water columns of 15 mid-sized rivers (discharge: 13.5–83.3 m3 s−1) spanning nutrient and total suspended solids gradients. We compared water column metabolic and nutrient uptake rates to reach-scale rates to estimate the contribution of the water column to the entire river. Water column metabolism was autotrophic on the day when measured, GPP increased with nutrient availability, and the water column contributed more to whole river GPP than to ER. Water column nutrient uptake increased with GPP across solutes, and there was a positive relationship between human land use and water column uptake of NO3−–N and SRP. The water column accounted for a substantial proportion of reach-scale metabolism and nutrient uptake, but this contribution depended on suspended material and nutrient availability. Integrating the water column into theory describing lotic ecosystem function should clarify mechanisms controlling metabolism and nutrient processing and enhance management of non-wadeable rivers. [ABSTRACT FROM AUTHOR]

Coastal wetlands of the Laurentian Great Lakes are vital habitats for biota of ecological and economic importance. These habitats are susceptible to water quality impairments driven by runoff from the landscape due to their location along the shoreline. Monitoring of the overall status of biotic and abiotic conditions of coastal wetlands within the Great Lakes has been ongoing for over a decade. Here, we utilize measurements of aquatic physicochemical and land cover variables from 877 vegetation zones in 511 coastal wetland sites spanning the US and Canadian shorelines of the entire Great Lakes basin. Our objective is to develop water quality indices based on physicochemical measures (Chem-Rank), land use/land cover (LULC-Rank), and their combined effects (Sum-Rank and Simplified Sum-Rank), for both vegetation zones and wetland sites. We found that water quality differed among wetland vegetation types and among Great Lakes regions, corroborating previous findings that human land use alters coastal wetland water quality. Future monitoring can use these straightforward, easy-to-calculate indices to assess the abiotic condition of aquatic habitats. Our data support the need for management efforts focused on reducing nutrient and pollution loads that stem from human activities, particularly in the developed southern portions of the Great Lakes basin. [ABSTRACT FROM AUTHOR]

In low‐gradient, macrophyte‐rich rivers, we expect that the significant change in macrophyte biomass among seasons will strongly influence both biological activity and hydraulic conditions resulting in significant effects on nutrient dynamics. Understanding seasonal variation will improve modelling of nutrient transport in river networks, including annual estimations of export, which could optimise decision‐making and management outcomes.We explored the relationships among seasonal differences in reach‐scale nutrient uptake, macrophyte abundance, solute transport and transient storage in the River Gudenå (Denmark), a large macrophyte‐rich river. We used the minimal pulse addition technique to measure uptake of ammonium, nitrate, soluble reactive phosphorus, as well as reach‐scale metabolism, and surface transient storage in spring, summer, and autumn.We found that riverine uptake changed among seasons and was linked to macrophyte biomass via both biological activity, reflected in reach‐scale metabolism, and through physical processes, as solute transport was influenced by longitudinal dispersion. In this macrophyte‐rich river, seasonal changes in macrophyte biomass affected contact time between the water and biota, which influenced ammonium and soluble reactive phosphorus uptake. Using stoichiometric scaling of reach‐scale metabolism, we found that seasonal variation also influenced the relative contributions of autotrophic and heterotrophic biota in assimilatory uptake.In summary, riverine nutrient uptake was not static, highlighting the importance of seasonality, with significant implications for modelling of nutrient export in river networks. Moreover, current management strategies that remove macrophyte biomass (i.e. weed cutting and dredging) will short‐circuit the positive effects of enhanced nutrient uptake resulting from abundant macrophytes in rivers. [ABSTRACT FROM AUTHOR]

Fluoxetine, a selective serotonin reuptake inhibitor (SSRI), is frequently detected in surface waters globally, yet the effects of SSRIs on ecological processes at environmentally realistic concentrations are not currently known. We used a controlled, replicated artificial stream experiment to expose biofilm, algal and stream insect communities to two different concentrations of fluoxetine: 20 ng/L (typical concentration detected in surface waters) and 20 µg/L (concentration shown to influence insect emergence and algal productivity). We quantified a range of community and ecosystem response metrics over the course of the 21d experiment including; algal biomass (chl-a), net ecosystem production (NEP), gross primary production (GPP), ecosystem respiration (ER) and invertebrate emergence. At 20 ng/L, fluoxetine significantly suppressed algal colonization on rocks, and reduced GPP after 13 days, but by day 21 chl-a, NEP and GPP did not differ between treatments and control. Fluoxetine increased ER on leaves where invertebrates were excluded, but had no effect on leaves accessible to invertebrates. Streams receiving 20 ng/L of fluoxetine had adult insects from the order Diptera emerge sooner and at a greater rate than control streams. Our results suggest that ecosystem function, including primary production and respiration, and invertebrate population dynamics are sensitive to SSRIs and that fluoxetine may alter these key processes concentrations found in the environment. [ABSTRACT FROM AUTHOR]

The faucet snail (Bithynia tentaculata) was introduced to the Great Lakes region in the late 1800s. Faucet snails alter native community dynamics and are an intermediate host for multiple trematode parasites that can be lethal to waterfowl when the snails are consumed. Although faucet snails have been established in the Great Lakes for over a century, their populations appear to have remained small for most of this period and their known distribution was limited to the lower Great Lakes, though basin-wide surveys were lacking until recently, so snails may have gone undetected. We compiled data from a five-year coastal wetland monitoring program spanning all of the Great Lakes, providing a basin-wide inventory of faucet snail populations and confirming the snail's presence in every Great Lake. Further, we identified potential drivers of faucet snail occurrence and abundance (individuals per sampling replicate) across the basin and within individual lakes to identify factors that could lead to elevated risk of range expansion. Across the basin and within individual lakes, faucet snail occurrence was related to human recreational transport (proximity to a boat launch) and eutrophication (anthropogenic land-use, elevated nutrient concentrations). In addition, at sites where faucet snails occurred, they were most abundant at wetlands with surrounding forest cover, suggesting that the species can thrive in a range of environmental conditions. Our results suggest that limiting passive transport of faucet snails is vital to minimizing their spread to remote wetlands where the snails may thrive once established. [ABSTRACT FROM AUTHOR]

The steadily rising global urban population has placed substantial strain on urban water quality, and this strain is projected to increase for the foreseeable future. Considerable attention has been given to the hydrological and physico‐chemical effects of urbanization on stream ecosystems. However, due to the relative infancy of the field of urban ecology, long‐term water quality analyses in urban streams are sparse. Using a 15‐yr stream chemistry monitoring record from Baltimore, Maryland, we quantified long‐term trends in nitrate, phosphate, total nitrogen, total phosphorus, chloride, and sulfate export at several sites along a rural–urban gradient. We found no significant change in solute export at most sites, although we did find specific patterns of interest for certain solutes. For example, nitrogen export declined at the most headwater urban site, while phosphorus export declined at the most downstream urban site. Coupling long‐term monitoring with data on gray and green infrastructure management throughout the landscape, we established relationships between solute export at the most downstream urban monitoring site and sanitary sewer overflows (SSOs), best management practice (BMP) implementation, and road salt application rates. Phosphorus export was correlated with BMP implementation in the watershed, whereas nitrogen export was related to SSOs. Despite highly urbanized watersheds, water quality does not appear to be declining at most of these sites, suggesting that current management may have limited further impairment. Results of our study suggest that both gray and green infrastructure are key for maintaining and improving water quality in this highly urbanized watershed. [ABSTRACT FROM AUTHOR]

Along the river network, water, sediment, and nutrients are transported, cycled, and altered by coupled hydrological and biogeochemical processes. Our current understanding of the rates and processes controlling the cycling and removal of dissolved inorganic nutrients in river networks is limited due to a lack of empirical measurements in large, (nonwadeable), rivers. The goal of this paper was to develop a coupled hydrological and biogeochemical process model to simulate nutrient uptake at the network scale during summer base flow conditions. The model was parameterized with literature values from headwater streams, and empirical measurements made in 15 rivers with varying hydrological, biological, and topographic characteristics, to simulate nutrient uptake at the network scale. We applied the coupled model to 15 catchments describing patterns in uptake for three different solutes to determine the role of rivers in network-scale nutrient cycling. Model simulation results, constrained by empirical data, suggested that rivers contributed proportionally more to nutrient removal than headwater streams given the fraction of their length represented in a network. In addition, variability of nutrient removal patterns among catchments was varied among solutes, and as expected, was influenced by nutrient concentration and discharge. Net ammonium uptake was not significantly correlated with any environmental descriptor. In contrast, net daily nitrate removal was linked to suspended chlorophyll a (an indicator of primary producers) and land use characteristics. Finally, suspended sediment characteristics and agricultural land use were correlated with net daily removal of soluble reactive phosphorus, likely reflecting abiotic sorption dynamics. Rivers are understudied relative to streams, and our model suggests that rivers can contribute more to network-scale nutrient removal than would be expected based upon their representative fraction of network channel length. [ABSTRACT FROM AUTHOR]

Urban streams are exposed to multiple different stressors on a regular basis, with increased hydrological flashiness representing a common urban stream stressor. Stream metabolism, the coupled ecosystem functions of gross primary production (GPP) and ecosystem respiration (ER), controls numerous other ecosystem functions and integrates multiple processes occurring within streams. We examined the effect of one large (Superstorm Sandy) and multiple small and moderately sized flood events in Baltimore, Maryland, to quantify the response and recovery of urban stream GPP and ER before and after floods of different magnitudes. We also compared GPP and ER before and after Superstorm Sandy to literature values. We found that both GPP and ER decreased dramatically immediately following floods of varying magnitudes, but on average GPP was more reduced than ER (80% and 66% average reduction in GPP and ER, respectively). Both GPP and ER recovered rapidly following floods within 4-18 d, and recovery intervals did not differ significantly between GPP and ER. During the two-week recovery following Superstorm Sandy, two urban streams exhibited a range of metabolic activity equivalent to ~15% of the entire range of GPP and ER reported in a recent meta-analysis of stream metabolism. Urban streams exhibit a substantial proportion of the natural variation in metabolism found across stream ecosystems over relatively short time scales. Not only does urbanization cause increased hydrological flashiness, it appears that metabolic activity in urban streams may be less resistant, but also more resilient to floods than in other streams draining undeveloped watersheds, which have been more studied. Our results show that antecedent conditions must be accounted for when drawing conclusions about stream metabolism measurements, and the rapid recovery and resilience of urban streams should be considered in watershed management and stream restoration strategies targeting ecosystem functions and services. [ABSTRACT FROM AUTHOR]

Background: Mesocosm experiments have become increasingly popular in climate change research as they bridge the gap between small-scale, less realistic, microcosm experiments, and large-scale, more complex, natural systems. Characteristics of aquatic mesocosm designs (e.g., mesocosm volume, study duration, and replication) vary widely, potentially affecting the magnitude and direction of effect sizes measured in experiments. In this global systematic review we aim to identify the type, direction and strength of climate warming effects on aquatic species, communities and ecosystems in mesocosm experiments. Furthermore, we will investigate the context-dependency of the observed effects on several a priori determined effect moderators (ecological and methodological). Our conclusions will provide recommendations for aquatic scientists designing mesocosm experiments, as well as guidelines for interpretation of experimental results by scientists, policy-makers and the general public. Methods: We will conduct a systematic search using multiple online databases to gather evidence from the scientific literature on the effects of warming experimentally tested in aquatic mesocosms. Data from relevant studies will be extracted and used in a random effects meta-analysis to estimate the overall effect sizes of warming experiments on species performance, biodiversity and ecosystem functions. Experimental characteristics (e.g., mesocosm size and shape, replication-level, experimental duration and design, biogeographic region, community type, crossed manipulation) will be further analysed using subgroup analyses. [ABSTRACT FROM AUTHOR]

Nitrogen (N) pollution of freshwater, estuarine and marine ecosystems is widespread and has numerous environmental and economic impacts. A portion of this excess N comes from urban watersheds comprised of natural and engineered ecosystems that can alter downstream N export. Studies of urban N cycling have focused on either specific ecosystems or on watershed-scale mass balances. Comparisons of specific N transformations across ecosystems are required to contextualize rates from individual studies. Here we reviewed urban N cycling in terrestrial, aquatic and engineered ecosystems, and compared N processing in these urban ecosystem types to native reference ecosystems. We found that net N mineralization and net nitrification rates were enhanced in urban forests and riparian zones relative to reference ecosystems. Denitrification was highly variable across urban ecosystem types, but no significant differences were found between urban and reference denitrification rates. When focusing on urban streams, ammonium uptake was more rapid than nitrate uptake in urban streams. Additionally, reduction of stormwater runoff coupled with potential decreases in N concentration suggests that green infrastructure may reduce downstream N export. Despite multiple environmental stressors in urban environments, ecosystems within urban watersheds can process and transform N at rates similar to or higher than reference ecosystems. [ABSTRACT FROM AUTHOR]

Benthic biofilms have multiple functions in stream and river ecosystems, and their growth and productivity are often limited by dissolved inorganic nutrient availability, particularly N or P. We deployed nutrient diffusing substrata (NDS) in 5 rivers in each of 3 regions: the Mountain West, the Arid West, and the Midwest, to assess regional and seasonal variation in nutrient limitation of river biofilms and to quantify which environmental factors control nutrient limitation. We constructed NDS with either inorganic or organic substrata to compare nutrient limitation of autotrophic and heterotrophic biofilms, and we explored inorganic N preference of biofilms by comparing results of NO3 - and NH4 + amendments. During summer deployments, autotrophic and heterotrophic biofilms in Mountain Western rivers were commonly limited by N or colimited by N and P, whereas nutrient limitation was less common in Arid Western and Midwestern rivers. We deployed NDS seasonally in Midwestern rivers and found no obvious seasonal patterns of nutrient limitation, probably because background nutrient concentrations were consistently high. Heterotrophic biofilm responses in Midwestern rivers suggested a preference for NO3 - over NH4 +. The magnitude of the autotrophic biofilm response, calculated as response ratios for gross primary production and chlorophyll a, were inversely related to % developed lands in the surrounding watershed and background NO3 - availability, whereas heterotrophic response ratios were related to river temperature. Patterns of nutrient limitation for autotrophic biofilms in rivers were similar to those in headwater streams, suggesting that biofilms in lotic ecosystems of varying size are similarly sensitive to nutrient amendments from the landscape. Clarifying the nutrient-limitation status of autotrophic and heterotrophic biofilms across a variety of rivers expands our understanding of nutrient limitation in lotic ecosystems and enables improved management of autotrophic and heterotrophic biofilms. [ABSTRACT FROM AUTHOR]

1. Adult Pacific salmon ( Oncorhynchus spp.) transport marine nutrients to fresh waters and disturb sediments during spawning. The relative importance of nutrient fertilisation and benthic disturbance by salmon spawners can be modulated by environmental conditions (e.g. biological, chemical and physical conditions in the catchment, including human land use). 2. To determine the importance of the environmental context in modifying the uptake and incorporation of salmon-derived material into stream biota, we measured the nitrogen (δ15N) and carbon (δ13C) isotopic composition of benthic algae (i.e. epilithon) and juvenile coho salmon ( Oncorhynchus kisutch) in seven streams across a timber-harvest gradient (8-69% catchment area harvested), both before and during the salmon run. Conditional bootstrap modelling simulations were used to assess variability in the response of epilithon and juvenile coho salmon to spawning salmon. 3. In response to spawning salmon, epilithon exhibited enrichment in both δ15N (mean: 1.5‰) and δ13C (2.3‰). Juvenile coho were also enriched in both δ15N (0.7‰) and δ13C (1.4‰). Conditional bootstrap models indicate decreased variation in data as spatial replication increases, suggesting that the number of study sites can influence the results of Pacific salmon isotope studies. 4. Epilithon isotopic enrichment was predicted by environmental conditions, with δ15N enrichment predicted by stream temperature and timber harvest ( R2 = 0.87) and δ13C enrichment by discharge, sediment size, timber harvest and spawner density ( R2 = 0.96). Furthermore, we found evidence for a legacy effect of salmon spawners, with pre-spawner δ15N and δ13C of both epilithon and juvenile coho predicted by salmon run size in the previous year. 5. Our results show that the degree of incorporation of salmon-derived nitrogen and carbon differs among streams. Furthermore, the environmental context, including putative legacy effects of spawning salmon, can influence background isotopic concentrations and utilisation of salmon-derived materials in southeast Alaska salmon streams. Future studies should consider the variation in isotopic composition of stream biota when deciding on the number of study sites and samples needed to generate meaningful results. [ABSTRACT FROM AUTHOR]

Anthropogenic N loadings and perturbations of macroconsumer communities impair ecological and economic services provided by streams. Organisms are adapted to natural disturbances, such as flooding and desiccation, but how anthropogenic and natural disturbances interact is poorly understood. We used large outdoor mesocosms to study the effect of , a common prairie headwater-stream minnow, and NH4++ additions (to simulate fish excretion) on the recovery of ecosystem structure and function following a flood, highlighting the potential for (and other macroconsumers) to affect denitrification. and NH4++ treatments differentially affected particulate organic matter size and filamentous algal structure. Ecosystem structure responded differently to mesocosm treatment over time, a result suggesting that grazers or NH4++-N availability may be especially important during early recovery periods. The presence of did not influence denitrification, but NH4++ additions altered the response of denitrifiers to nutrient and energy amendments, and denitrification rates decreased following the recovery of mesocosms. Temporal changes in denitrification probably were caused by increasing hyporheic dissolved O2 concentrations, which led to potentially fewer anoxic microsites for production of denitrification enzymes. Our study shows that grazers affect the recovery of ecosystem structure, but denitrification in the context of these prairie-stream mesocosms appears to be unaffected by . [ABSTRACT FROM AUTHOR]

The continually increasing global population residing in urban landscapes impacts numerous ecosystem functions and services provided by urban streams. Urban stream restoration is often employed to offset these impacts and conserve or enhance the various functions and services these streams provide. Despite the assumption that "if you build it, [the function] will come," current understanding of the effects of urban stream restoration on stream ecosystem functions are based on short term studies that may not capture variation in restoration effectiveness over time. We quantified the impact of stream restoration on nutrient and energy dynamics of urban streams by studying 10 urban stream reaches (five restored, five unrestored) in the Baltimore, Maryland, USA, region over a two‐year period. We measured gross primary production (GPP) and ecosystem respiration (ER) at the whole‐stream scale continuously throughout the study and nitrate (NO3−‐N) spiraling rates seasonally (spring, summer, autumn) across all reaches. There was no significant restoration effect on NO3−‐N spiraling across reaches. However, there was a significant canopy cover effect on NO3−‐N spiraling, and directly comparing paired sets of unrestored‐restored reaches showed that restoration does affect NO3−‐N spiraling after accounting for other environmental variation. Furthermore, there was a change in GPP : ER seasonality, with restored and open‐canopied reaches exhibiting higher GPP : ER during summer. The restoration effect, though, appears contingent upon altered canopy cover, which is likely to be a temporary effect of restoration and is a driver of multiple ecosystem services, e.g., habitat, riparian nutrient processing. Our results suggest that decision‐making about stream restoration, including evaluations of nutrient benefits, clearly needs to consider spatial and temporal dynamics of canopy cover and trade‐offs among multiple ecosystem services. [ABSTRACT FROM AUTHOR]