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Nutrients and contaminants in wastes from seabird colonies can dramatically alter surrounding vegetation, water chemistry, and aquatic communities. Here we examine the effects of nesting Common Eiders (Somateria mollissima) on diatom assemblages from 21 ponds on islands in Hudson Strait, sub-Arctic Canada (63°12′N, 76°52′W). A total of 116 diatom taxa were identified, with assemblages dominated by benthic Diatoma and Nitzschia species typical of freshwater ponds influenced by seabird colonies. Canonical correspondence analysis (CCA), with forward selection and Monte Carlo permutation tests (999 repetitions), identified parameters correlated to seabird inputs, including specific conductivity, Al, and Cd concentrations, as the variables most closely linked to diatom species composition. A diatom-based conductivity inference model was developed using a weighted average with partial least squares (WA-PLS) model (r2boot = 0.723; RMSEP = 0.544) to describe the conductivity optima of the most commonly encountered taxa. Although we found increased numbers of eutrophilous taxa in highly eider-influenced ponds, the diatom assemblages were primarily influenced by conductivity, which was primarily linked to ocean spray, and statistical tests did not identify significant differences between the taxa of high and low eider-influenced sites (ANOSIM; p = 0.429; r = 0.009). This calibration set exhibits the potential use of diatoms as indicators of seabird abundance and density across breeding sites; however, in coastal ponds, ocean spray (and hence conductivity) appears to be a confounding factor affecting diatom assemblages.

Marked increases in ring-billed gulls and double-crested cormorants in the Laurentian Great Lakes during the last century have garnered attention over their ecological impacts, sparking debates about management strategies. However, monitoring data are generally sparse and of short duration for these colonies, hampering the ability to place recent changes within long-term context. Sediment records from ponds immediately surrounded by colonies on nesting islands can be used to track past bird populations, as they release wastes with geochemical signals that can be tracked using traditional paleolimnological methods, such as diatoms and stable isotopes of nitrogen (δ15N). Here, we provide new information about waterbird nesting histories on islands in eastern Lake Ontario that are of interest to wildlife managers. In all bird-impacted ponds, eutrophic diatom assemblages and elevated sediment chlorophyll-a coincided with high signatures of δ15N in the recent sediments, signifying bird influence. An absence of significant bird impacts in the oldest portion of one sediment core indicates that the current cormorant colony size (>2000 birds) is unprecedented over the ~150-year record. Diatoms and sediment chlorophyll-a also responded to even a small, short-duration cormorant nesting event on an actively managed reference island. Collating our findings with those from four previously studied sediment cores from nearby islands, we show that cormorants are unlikely to have occupied eastern Lake Ontario in their current numbers within the past ~150 years. However, ring-billed gulls have likely used several islands in the area for most of the 20th century (and perhaps earlier) until present.

Significance The paucity of monitoring data for seabird populations at suitable temporal and spatial scales challenges the development of realistic and effective conservation policies. We employ newly developed paleoenvironmental techniques at 10 key subarctic seaduck colonies to reconstruct broadscale population changes at decadal timescales through the 20th century. We show that harvesting practices in southwestern Greenland and northeastern Canada were unsustainable, timed with the advent of widespread use of shotguns and outboard motors for hunting across the North. Our historical population reconstructions, corroborated with two independent proxies (sterols and stable nitrogen isotopes), reaffirms that hunting restrictions were necessary to prevent the collapse of this subspecies., Where available, census data on seabirds often do not extend beyond a few years or decades, challenging our ability to identify drivers of population change and to develop conservation policies. Here, we reconstruct long-term population dynamics of northern common eiders (Somateria mollissima borealis). We analyzed sterols together with stable nitrogen isotopes in dated pond sediment cores to show that eiders underwent broadscale population declines over the 20th century at Canadian subarctic breeding sites. Likely, a rapidly growing Greenland population, combined with relocation of Inuit to larger Arctic communities and associated increases in the availability of firearms and motors during the early to mid-20th century, generated more efficient hunting practices, which in turn reduced the number of adult eiders breeding at Canadian nesting islands. Our paleolimnological approach highlights that current and local monitoring windows for many sensitive seabird species may be inadequate for making key conservation decisions.

Seabirds are thought to provide ecological services such as the movement of nutrients between marine and terrestrial ecosystems, which may be especially critical to productivity and diversity in nutrient-poor environments. Most Arctic ecosystems are unaffected by local human impacts and are naturally nutrient poor and especially sensitive to warming. Here, we assessed the effects of nesting common eider ducks (Somateria mollissima) on soil, vegetation, and pond sediments on island archipelagoes in Hudson Strait between Nunavut and Québec, Canada. Soil, moss, and pond sediments were significantly higher in nitrogen on islands with large numbers of nesting eiders compared to sites with no nesting birds. The highest concentrations of nitrogen in soils and moss occurred at the margins of ponds on eider islands, which correspond to the areas of highest eider use. δ15N and δ34S values in soils, moss, and sediments indicated substantial marine-derived organic matter inputs at the higher nutrient sites. We propose that by foraging on coastal marine benthic invertebrates and returning to islands to nest, eider ducks bio-transport and concentrate marine-derived nutrients to their colony islands, fertilizing Arctic island ecosystems in the process. As common eiders nest on thousands of low to mid-latitude islands throughout the circumpolar Arctic, these nutrient inputs likely dramatically affect biota and ecosystem functioning throughout the tundra biome.

The extensive peatlands and lakes of the Far North of Ontario warrant committed scientific attention given their status as a significant carbon sink. Economic interest in this region has recently increased due to the discovery of vast mineral deposits (mainly chromite and nickel) known as the “Ring of Fire”. Mineral exploration and infrastructure planning are underway, but environmental monitoring is only beginning. Detailed baseline ecological information is required to assess the impacts of future resource extraction within the context of multiple environmental stressors (including recent regional climate warming). Here we use sediment cores from two relatively deep lakes (Zmax ~ 10 m) and two shallow lakes (Zmax ~ 2 m), all located in the vicinity of the Ring of Fire, to examine biotic responses to warming prior to the commencement of mining activities. Our data show that, over the past ~150 years, diatom and cladoceran sedimentary assemblages have transitioned from dominance by littoral/benthic forms to greater abundances of planktonic cladoceran (an increase of ~3 to 34 %) and diatom taxa (an increase of ~3 to 22 %). Increased relative abundances of planktonic taxa are consistent with warming-induced changes in lake properties including longer ice-free periods and increased production by planktonic algae. The response of diatom assemblages in shallow lakes to warming preceded the deeper lakes by ~45 to 60 years, and substantial increases in aquatic production (~4 to 15 times higher than in sediments deposited prior to 1900) were observed in the shallow lakes, in agreement with previous analyses demonstrating the heightened sensitivity of shallow systems to climate warming. These data provide important information necessary to distinguish potential ecological impacts related to resource extraction from natural variation and the ongoing responses to regional climate warming.

Human activities can greatly affect the chemical and biological composition of High Arctic lakes that otherwise receive only sparse inputs from their watersheds and airsheds. This paper reports a study of three High Arctic waterbodies in which wastewater from an airport was released over the span of several decades. Using sediment cores from these waterbodies, we reconstructed the history of wastewater inputs using a multiproxy approach consisting of sterols, stanols, metals, and stable isotopes of carbon and nitrogen. This multi-proxy approach showed good concordance between δ15N, coprostanol (a stanol specific to human faecal sources), cholesterol, and cholestanol, which tracked the known history of human wastewater deposition to this High Arctic environment. Concentrations of plant derived sterols, such as campesterol and sitosterol, increased at the time of wastewater input, presumably due to increased plant growth stimulated by wastewater nutrients. Metal(loid)s normalized to titanium showed that copper and lead tracked the input of wastewater into one pond (R-12), while arsenic, cadmium, chromium, nickel, and zinc increased more than 15 years after the onset of wastewater input. These results demonstrated the ability of sterols and stanols to reconstruct the historical presence of humans in High Arctic locations within the last 80 years. They provided compelling evidence that these paleolimnological approaches may be useful to track the occupation of Arctic peoples beyond the last century.

This study evaluates the presence of metal(loid) contamination from shrimp aquaculture effluent in a nearby mangrove ecosystem in Khung Krabaen Bay (KKB), Thailand. Our objectives were to: 1) examine how sediment metal(loid) concentrations change spatially in KKB relative to the aquaculture ponds; (2) compare mollusc trophic dynamics of elements associated with shrimp aquaculture; and (3) determine if certain mangrove mollusc species present better ecological indicators of aquaculture elemental contamination. We analyzed targeted elemental concentrations (As, Mn, Cu, Zn, Cr, Pb) in sediments sampled at increasing distance from intensive shrimp aquaculture and within the tissues of five species of molluscs. Differences in mollusc diet were studied using carbon (ẟ13C) and nitrogen (ẟ15N) stable isotopes, and biomagnification and biodilution of metal(loid)s were examined using ẟ15N values to infer trophic position. Elemental concentrations were low in farmed shrimp and pellet food relative to mangrove molluscs, but high in the sediments of drainage ponds filtering pond effluent. Declining elemental concentrations from the aquaculture drainage ponds to the mangrove sediments closest to shrimp farms suggested that the management settling ponds are effective at attenuating metal(loid) contamination. Large differences in mollusc mean ẟ13C (–25.8 to –20.1‰) and ẟ15N (1.9 to 8.3‰) values indicate variable diets across species, and trophically-elevated molluscs had greater marine-based diets resulting in a significant, positive correlation between mollusc ẟ13C and ẟ15N values. KKB molluscs biomagnify As, Zn, and Se, whereas declines in Mn and Cu with increasing trophic position indicate biodilution. The metals Pb, Fe, Al, Cr were elevated in the shrimp drainage pond sediments and in the tissues of the gastropods Ellobium aurisjudae, Cerithidea obtusa (both mud grazing), and Nerita lineata (algal grazing at low tide), identifying these gastropod species as probable bioindicators of aquaculture contamination in southeast Asian mangroves. Although we find biomagnification of some elements, mangrove mollusc metal(loid) concentrations are not likely to be of toxicological concern, and in fact, were lower than many mangroves elsewhere impacted by industrial and sewage contamination.

Arctic freshwater ponds are typically pristine and oligotrophic, however seabird biovectors can markedly alter water quality via enrichment with marine-derived nutrients and bioaccumulated metals. These ornithogenic inputs can be the dominant factor structuring aquatic biota and the surrounding island flora. Here, we measured a suite of limnological water chemistry variables and sediment geochemistry from 21 freshwater ponds influenced by Common Eiders (Somateria mollissima) in Hudson Strait, near the northern communities of Cape Dorset (Nunavut) and Ivujivik (Quebec). Nest counts and sedimentary δ15N values were used as proxies of bird abundance. Nutrient-rich guano from the nesting eiders visibly promoted the growth of catchment vegetation. Elevated metal (Al, Cd, Zn), metalloid (Se), and nutrient concentrations (N, P) in the water of eider-affected sites were recorded (Sign test; p = 0.004), but the proximity of many sites to the coast meant that variables related to ocean spray (conductivity, Na+, Mg2+, Cl−, Sr) confounded the effects of birds on pond water chemistry. In contrast, sediment geochemistry appeared to more clearly characterize sites according to the level of eider activity in their catchments by tracking Pb, Cd, N, and P sedimentary concentrations (Sign test; p = 0.02). These results have direct implications for reconstructing historical eider population trends using sediment archives, which is necessary to inform effective conservation management strategies.

Niven Lake was the first wastewater disposal site for the City of Yellowknife (Northwest Territories, Canada), receiving domestic sewage for more than 30 years. Here, we used a high-resolution sediment core to track past sewage inputs to Niven Lake by comparing changes in sedimentary sterols and three diagnostic ratios for human fecal contamination, as well as biological assemblages and overall lake production, with the known history of sewage inputs to the lake from 1948 to 1981. Coprostanol, often considered the best indicator of human fecal contamination, increased by ~8% between depths of 7.5 cm and 5 cm (~1950 to 1981) and was more reliable in tracking sewage contamination than diagnostic sterol ratios. Muted responses in subfossil diatom and chironomid assemblages were noted during the time of sewage inputs, and similar responses have been reported in other eutrophic Arctic sites, as well as in many macrophyte-dominated shallow lakes in general. More marked shifts in diatoms and chironomids occurred a decade after the end of sewage inputs, in the 1990s, a time that closely aligned with the warmest years on record for Yellowknife. This post–sewage era response was indicative of anoxia and possibly of positive feedback from internal phosphorus loading. The response may have been facilitated by recent climate warming, resulting in a lagging recovery from eutrophication. Changes in the diatoms and chironomids of Niven Lake were also indicative of metal pollution, suggesting that the lake has experienced the compounding effects of arsenic contamination from nearby gold mining.

A comprehensive field and modeling study indicates vulnerability of tidal wetlands to sea-level rise on the U.S. Pacific coast., We used a first-of-its-kind comprehensive scenario approach to evaluate both the vertical and horizontal response of tidal wetlands to projected changes in the rate of sea-level rise (SLR) across 14 estuaries along the Pacific coast of the continental United States. Throughout the U.S. Pacific region, we found that tidal wetlands are highly vulnerable to end-of-century submergence, with resulting extensive loss of habitat. Using higher-range SLR scenarios, all high and middle marsh habitats were lost, with 83% of current tidal wetlands transitioning to unvegetated habitats by 2110. The wetland area lost was greater in California and Oregon (100%) but still severe in Washington, with 68% submerged by the end of the century. The only wetland habitat remaining at the end of the century was low marsh under higher-range SLR rates. Tidal wetland loss was also likely under more conservative SLR scenarios, including loss of 95% of high marsh and 60% of middle marsh habitats by the end of the century. Horizontal migration of most wetlands was constrained by coastal development or steep topography, with just two wetland sites having sufficient upland space for migration and the possibility for nearly 1:1 replacement, making SLR threats particularly high in this region and generally undocumented. With low vertical accretion rates and little upland migration space, Pacific coast tidal wetlands are at imminent risk of submergence with projected rates of rapid SLR.

Peatlands in northern Ontario, Canada, archive multiple biological indicators, including macrofossils, algae, testate amoebae, and pollen. These proxies can provide insights concerning the timing and nature of long-term climatic and environmental changes. The Hudson Bay Lowlands (HBL) of central Canada contain one of Earth’s largest continuous peatland complexes, and thus comprehensive spatial and temporal studies are needed to understand the implications of climate change on carbon cycling. Diatom assemblages were examined in three cores retrieved from ombrotrophic bogs across two Canadian terrestrial ecozones. Comparisons were made with testate amoebae and macrofossil data previously analyzed from these cores, as well as with regional pollen records from surrounding peatlands. From ~2000 to ~600 cal. BP, changes in diatom composition likely reflect hydrosere succession within the peatland, including fluctuations in connectivity to the water table and pH changes. From ~600 cal. BP to present, the synchronous timing of changes in diatoms and testate amoebae are tracking drying conditions and subsequent microhabitat variations that occur within bogs. It is possible that diatoms are tracking subtle changes in the stability of peat microforms including bog hollows and hummocks, highlighting their sensitivity to small chemical change, whereas testate amoebae are tracking the lowering of a peatland water table and subsequent drying of the peatland. The use of multiple proxies provides a more holistic approach to interpreting past ecological succession and responses to climate within peatlands. When present and well preserved, diatoms can be applied to track drying conditions in bogs, in terms of both hydrosere succession and present climatic change.

A multi-proxy paleolimnological survey was performed on 13 lakes in the Hudson Bay Lowlands (HBL) of northern Ontario in order to provide a regional analysis of recent environmental changes in this poorly studied sub-Arctic region. In contrast to the amplified warming experienced by most of the circumpolar Arctic since the mid-19th century, the climate of the Hudson Bay (HB) region has remained relatively cool and stable for hundreds of years. However, since approximately the 1990s, the HBL has experienced rapid and large increases in air temperature and declines in sea ice. Diatom, cladoceran, and chironomid remains preserved in the recent (surface) and pre-1850 sediments of 13 lakes were used to examine whether this new climate regime has resulted in species assemblage changes across multiple trophic levels. Our results indicate clear limnological responses to warming among the freshwater biota of HBL lakes; however, the magnitude of this change varied among both biological indicators and sites...

Seabirds that congregate in large numbers during the breeding season concentrate marine-derived nutrients to their terrestrial nesting sites, and these nutrients disperse and enhance production in nearby terrestrial, freshwater and marine ecosystems. In the Canadian Arctic, large seabird colonies (>100,000 breeding pairs) nest on cliff faces that drain directly in the ocean, ultimately returning the nutrients back to the marine environment from which they were derived. However, strong winds blowing up cliff faces could transport nutrients up in elevation and onto surrounding terrestrial and aquatic environments. Here, we assess the degree to which seabird nutrients and metals have been delivered to coastal lakes near Hudson Strait (Nunavut, Canada) over the past century. Three lakes located at a higher elevation and increasing distance from a thick-billed murre (Uria lomvia) colony (~400,000 breeding pairs) were sampled for surface water chemistry. In addition, algal assemblages, nitrogen isotopes, and metal/metalloids were analyzed in four dated sediment cores. Elevated nutrients and major ions, as well as an enriched δ15N signature in the sediment cores, were measured in the lake 1km from the seabird colony. In contrast, similar oligotrophic and benthic diatom assemblages were identified in all three lakes, suggesting that diatoms were not influenced by enhanced nutrient inputs in this Arctic environment. Chemical tracers (e.g., total mercury) and algal assemblages in the lake near the colony suggest climate warming since ~1950 was the most likely driver of limnological changes, but this effect was muted in the more distant lakes. These pronounced changes in the seabird-impacted lake suggest that, with warming air temperatures and diminished lake ice cover, longer growing seasons may allow for aquatic organisms to more fully exploit the seabird nutrient subsidies.

The overall goal of this study was to quantify the major and minor sources and losses of total phosphorus (TP) to the Lake of the Woods (LOW), summarized as a nutrient budget. This research was initiated in response to degradation in lake water quality, including elevated TP concentrations and increased cyanobacterial blooms, which has resulted in LOW's classification as an “Impaired Waterbody” in Minnesota. The whole-lake LOW TP budget shows that tributary inflow is largely dominated by a single source, the Rainy River, draining 79% of the LOW catchment by area. Currently, there is only a small TP contribution from shoreline residential developments (6 t; ~ 1%) at a whole-lake scale, relative to the large TP loads from atmospheric deposition (95 ± 55 t; 13%) and the Rainy River (568 ± 186 t; 75%). Overall, the annual TP load to LOW was ~ 754 t with ~ 54% TP retained within the lake. The nutrient budget for the Rainy River catchment revealed that contributions from point sources along the river constitute the largest anthropogenic TP source to the Rainy River and eventually to LOW. Historical load calculations along the Rainy River show that this load has been significantly reduced since the 1970s, and presently just over 100 t of P enters LOW from anthropogenic point sources. These TP budgets provide insights into the major sources of TP influencing the overall LOW water quality and with future refinement may provide a greater understanding of linkages between TP loading and spatial and temporal water quality changes in the LOW.

Animal body size is a driving force behind trophic interactions within biological communities, yet few studies have explored relationships between body size and trophic position (based on δ15N) at a broad-scale in freshwater lakes. Therefore, our goals were to (1) determine whether body size is a good predictor of trophic position for multiple pelagic zooplankton taxa and fish communities, and (2) examine how body size-trophic position relationships at the community level compare to species level for fish. Zooplankton and fish were collected from 12 and 7 lakes, respectively, located in the Kawarthas, southern Ontario, Canada. The results indicated that for zooplankton, significant positive but different relationships were found between body size and trophic position for cladocerans, in general, and Daphnia, but not Holopedium. For fish, at the lake community level six out of seven relationships were positive and significant, but again, different among lakes. In contrast, at the species level only three of eight species-specific relationships were significant. Furthermore, for two widespread species, Perca flavescens and Micropterus dolomieu, significant differences were found between community- and lake-specific species relationships. Our community-level models and most species-level models provide evidence that trophic interactions in freshwater lakes are size-based. These results demonstrate that general species models should be applied with caution when using body size to predict trophic position. Additionally, the predictive power of some relationships found here is questionable since, albeit significant, their strengths are generally low. Together, our results suggest that body size may have limited use in predicting trophic position of some biota in temperate freshwater lakes.

Paleolimnological approaches were used to assess the ecological and environmental implications of diatom assemblage compositional changes recorded over the last , 200 yr from four sites in the Lake of the Woods (LoW), Ontario, Canada. Comparisons between a reference site (Whitefish Bay) and three disturbed sites (Bigstone Bay, Paleolimnological Project site No. 1, and Forrest Island) provide insights into the effects that multiple stressors (dam construction, total phosphorus [TP] changes, and recent warming) have had on the ecology of this highly complex freshwater system. Overall patterns of diatom compositional changes from highresolution 210Pb-dated sediment cores revealed a strong temporal coherence ca. 1910 and then again over the last few decades among all sites. Hydromanagement activities at the turn of the 19th century and recent warming over the last few decades played key roles in the LoW diatom changes. Diatom compositional changes at all sites were significantly related to trends in nearby air temperature records over the past century and to changes in lake ice phenology over the past , 40 yr from Whitefish Bay. Turn-of-the-century hydromanagement activities do not appear to have had long-term effects on diatom-inferred TP (DI-TP), particularly at the disturbed sites. Clear decreases in DI-TP over the last few decades were evident at all sites, but at the reference site these decreases were well below pre-disturbance levels, which we link in part to recent warming. Substantial changes in climate will amplify the effects of multiple stressors on lake water properties that have major implications on algal communities.

With the expansion of urban centres in the mid-twentieth century and the post-1970 decrease in pesticides, populations of double-crested cormorants ( Phalacrocorax auritus ) and ring-billed gulls ( Larus delawarensis ) around Lake Ontario (Canada and USA) have rapidly rebounded, possibly to unprecedented numbers. Along with the use of traditional palaeolimnological methods (e.g. stable isotopes, biological proxies), we now have the capacity to develop specific markers for directly tracking the presence of waterbirds on nesting islands. Here, we apply the use of lipophilic sterols and stanols from both plant and animal-faecal origins as a reliable technique, independent of traditional isotopic methods, for pinpointing waterbird arrival and population growth over decadal timescales. Sterol and stanol concentrations measured in the guano samples of waterbird species were highly variable within a species and between the three species of waterbirds examined. However, cholesterol was the dominant sterol in guano, and phytosterols were also high in ring-billed gull guano. This variability highlights a specialist piscivorous diet for cormorants compared to a generalist, omnivorous diet for gulls, which may now often include grain and invertebrates from agricultural fields. A ratio that includes cholesterol and sitosterol plus their aerobically reduced products (cholestanol, stigmastanol) best explained the present range of bird abundance across the islands and was significantly correlated to sedimentary δ 15 N. Overall, we demonstrate the use of sterols and stanols as a direct means for tracking the spatial and temporal presence of waterbirds on islands across Lake Ontario, and probably elsewhere.

Giant Mine, located in the city of Yellowknife (Northwest Territories, Canada), is a dramatic example of subarctic legacy contamination from mining activities, with remediation costs projected to exceed $1 billion. Operational between 1948 and 2004, gold extraction at Giant Mine released large quantities of arsenic and metals from the roasting of arsenopyrite ore. We examined the long-term ecological effects of roaster emissions on Pocket Lake, a small lake at the edge of the Giant Mine lease boundary, using a spectrum of palaeoenvironmental approaches. A dated sedimentary profile tracked striking increases (approx. 1700%) in arsenic concentrations coeval with the initiation of Giant Mine operations. Large increases in mercury, antimony and lead also occurred. Synchronous changes in biological indicator assemblages from multiple aquatic trophic levels, in both benthic and pelagic habitats, indicate dramatic ecological responses to extreme metal(loid) contamination. At the peak of contamination, all Cladocera, a keystone group of primary consumers, as well as all planktonic diatoms, were functionally lost from the sediment record. No biological recovery has been inferred, despite the fact that the bulk of metal(loid) emissions occurred more than 50 years ago, and the cessation of all ore-roasting activities in Yellowknife in 1999.