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Vallisneria americana (Tape-grass) in the lower St. Johns River, FL, is exposed to variability in salinity and turbidity. From 2002 to 2011, we compared mean blade length, plant depth, and bed width between residential and natural shorelines, the western and eastern sides, and river sections of 64–80 km, 81–96 km, and 97–112 km from the river mouth. Leaf blades of eastern plants were 27.0 cm longer and were found in 0.57 m greater depths, a pattern possibly related to seasonal westerly winds. We observed no differences with land use. Blades were 20.0 cm longer in the farthest section where salinity concentrations were 1.35 ppt lower than in the 64–80 km section. Following hurricanes, resilience depended on pre-storm bed health and post-storm water quality.

Harmful algal blooms are a growing human and environmental health hazard globally. Eco-physiological diversity of the cyanobacteria genera that make up these blooms creates challenges for water managers tasked with controlling the intensity and frequency of blooms, particularly of harmful taxa (e.g., toxin producers, N2 fixers). Compounding these challenges is the ongoing debate over the efficacy of nutrient management strategies (phosphorus-only versus nitrogen and phosphorus), which increases decision-making uncertainty. To improve our understanding of how different cyanobacteria respond to nutrient levels and other biophysical factors, we analyzed a unique 17 year data set comprising monthly observations of cyanobacteria genera and zooplankton abundances, water quality, and flow in a bloom-impacted, subtropical, flow-through lake in Florida (United States). Using the Random Forests machine learning algorithm, an ensemble modeling approach, we characterized and quantified relationships among environment...

Trent T, Hendrickson J, Harwell MC. 2017. A rapid, cost-effective screening tool for measuring Chl-a in water samples. Lake Reserv Manage. 00:1–6A rapid, cost-effective method for assessing chlorophyll a (Chl-a) concentrations in freshwater streams and lakes can provide an important screening tool for tracking algal blooms. While the laboratory analysis of field samples by spectrophotometer or high-performance liquid chromatography remains the optimal method for characterizing phytoplankton photosynthetic pigments, laboratory analysis can be time- and cost-prohibitive when collecting numerous samples to assess spatial or temporal aspects of a bloom. In 2011, we explored the utility of an inexpensive hand-held chlorophyll content meter (CCM; CCM-200 plus, Opti-Sciences, Inc.), normally used for leaf chlorophyll measurements, to assess Chl-a in water samples from the lower St. Johns River. CCM measurements were made on microfiber filter paper through which 200–600 mL of river water had been filtered...

Seasonal patterns in factors that affect primary producers are an important part of defining the structure and function of aquatic ecosystems. However, defining seasonality is often more difficult in aquatic than in terrestrial ecosystems, particularly in subtropical and tropical environments. In this study, a long-term data set for a shallow subtropical lake (Lake George, Florida, USA) was used to investigate seasonality using a range of physical, chemical and hydrological parameters. K-means cluster analysis of monthly averages among 11 selected environmental factors across 18 years suggested the overall annual pattern consists of three different seasonal clusters: a cold season (January–April), a warm season (May–August) and a flushing season (September–December). High dissolved oxygen and increased Secchi depth are key features of the cold season, while the warm season is characterized by high mean light irradiances, temperature, rainfalls, total nitrogen and phytoplankton biomass (as chlorophyll a level). The flushing season is characterized by high river discharge rates and high levels of dissolved nutrients and colored organic matter. Multiple response permutation procedures indicated that these seasonal cluster arrangements were significantly different than randomly permuted clusters (A-statistics = 0.3314, significance of delta = 0.0160, based on 1000 permutations). Results from principal component analyses supported the presence of the three seasons in the lake. Linear models explaining chlorophyll a levels using the 3-season system generally indicated better ratios of explained variance compared to the models without seasonal alignments, further indicating that even for sub-tropical systems defining seasons provides a better understanding of phytoplankton dynamics. The approaches used in this study provide statistically-based multivariate tools for the definition of seasonality in aquatic ecosystems. The ability to accurately define seasons is a key step in modeling the structure and dynamics of aquatic ecosystem, which is essential to the development of effective management strategies in a rapidly changing world.

An 18-year data set (1993–2010) of water column variables from Lake George, Florida (USA), was used to examine relationships between the phytoplankton community (composition and biomass) and physical variables (temperature and hydrologic discharge rates). Lake George is a large shallow eutrophic lake located in the subtropical environment of north Florida and is subject to frequent and intense blooms of cyanobacteria. Cyanobacteria dominated the phytoplankton community during warmer months of the year (May–September). Other phytoplankton taxa increased their relative contributions to phytoplankton biomass during the colder months (November–March), when cyanobacterial biomass was low. Increased discharge rates during the peak flushing season (September–December) were correlated to diminished cyanobacterial biomass despite elevated nutrient levels. Analysis of time series data revealed higher warm season peaks in cyanobacteria biomass during years of relatively low discharge, whereas other phytoplankton groups showed the opposite trend with peaks during the colder months. These observations indicate a need for lake management strategies that consider both hydrologic and nutrient loadings within the context of possible future changes in temperature and rainfall regimes.

The cyanobacteria index (CI) has been applied to Medium Resolution Imaging Spectrometer (MERIS) imagery to characterize cyanobacterial biomass in diverse regions. While a consistent qualitative estimate of cyanobacterial biomass is useful, establishing universal relationships to chlorophyll a (chl) concentration, the dominant photosynthetic pigment in phytoplankton, would quantify blooms for regional comparisons. Relationships between chl concentrations were determined from water reflectance measurements and chl concentration from water samples taken from cyanobacterial blooms in eutrophic lakes in Florida, where chl ranged from 16 to 115 µg L−1. When the chl relationship was applied to simultaneous satellite and field data, the chl concentration determined from satellite CI showed negligible bias and root mean square error of 27%. The generic CI-based chl algorithm presented here seems suitable for consistent quantification of chl concentration within cyanobacterial blooms.

In the summer of 2010, a sustained multispecies fish kill, affecting primarily adult red drum (Sciaenops ocellatus) and Atlantic stingray (Dasyatis sabina), along with various baitfish such as menhaden (Brevoortia spp.) and shad (Dorosoma spp.), was documented for six weeks along 50 km of the Lower St. Johns River (LSJR), Florida. An Aphanizomenon flos-aquae bloom was present in the freshwater reaches before the fish kill. The kill was triggered by a significant reverse-flow event and sudden influx of high-salinity water in late May that contributed to the collapse of the bloom upstream and brought euryhaline fish downstream into the vicinity of the senescing bloom or its by-products. The decomposing bloom led to a sequence of events, including the release of small amounts of cyanotoxins, bacterial lysis of cyanobacterial cells, high organic loading, and changes in the diversity and dominance of the plankton community to include Microcystis spp., Leptolyngbya sp., Pseudanabaena spp., Planktolyngbya spp., and low concentrations of Heterosigma akashiwo. Dissolved oxygen levels were within normal ranges in the reach of the fish kill, although elevated ammonia concentrations and high pH were detected farther upstream. These conditions resulted in complex pathological changes in fish that were not consistent with acute cyanotoxin exposure or with poor water quality but were attributable to chronic lethal hemolysis. Potential sources of hemolytic activity included H. akashiwo, Microcystis spp., and Bacillus cereus, a hemolytic bacterium. The continued presence of A. flos-aquae in the LSJR could have significant environmental repercussions and ideally the causal factors contributing to bloom growth and maintenance should be fully understood and managed.

Cross-shore exchange by strong (cross-shore wind stress, τsx>0.05 Pa) diurnal (7–25 h) sea breeze events are investigated using two years of continuous wind, wave, and ocean velocity profiles in 13 m water depth on the inner-shelf in Marina, Monterey bay, California. The diurnal surface wind stress, waves, and currents have spectral peaks at 1, 2, and 3 cpd and the diurnal variability represents about 50% of the total variability. During sea breeze relaxation (−0.05 0.05 Pa), a uniform offshore profile develops that is different from the background undertow profile allowing cross-shore Lagrangian transport to develop, while including Lagrangian Stokes drift. The diurnal cross-shore current response is similar to subtidal (>25 h) cross-shore current response, as found by Fewings et al. (2008) . The seasonality of waves and winds modify the diurnal sea breeze impact. It is suggested that material is not transported cross-shore except during sea breeze events owing to near zero transport during relaxation periods. During sea breeze events, cross-shore exchange of material appears to occur onshore near the surface and offshore near the sea bed. Since sea breeze events last for a few hours, the long-term cross-shore transport is incremental each day.

Summary 1. The effect of variability in rainfall on the potential for algal blooms was examined for the St Johns River in northeast Florida. Water chemistry and phytoplankton data were collected at selected sites monthly from 1993 through 2003. Information on rainfall and estimates of water turnover rates were used in the analyses of trends in phytoplankton biomass. 2. Major trends in rainfall and runoff within the lower St Johns River catchment over the 10-year study period were marked by both significant drought and flood periods. Autumn and winter rainfall patterns were strongly correlated with the range of Pacific sea surface temperature anomalies associated with El Nino events and La Nina periods. The effect of these major shifts in rainfall was evident in the strong relationship to replacement rates for water within the lower St Johns River. 3. The eutrophic status of the river was reflected in the high concentrations of nitrogen and phosphorus observed at all sampling sites, with total nitrogen concentrations up to 3100 μg L−1 and total phosphorus concentrations up to 180 μg L−1. 4. While it is clear that the high phytoplankton biomass and frequent blooms that characterize the freshwater portions of the lower St Johns River are fundamentally based on nutrient status, the expression of that potential was strongly correlated to water replacement rates, as revealed by the inverse relationship between phytoplankton biovolume increase and water turnover rate, with an R2 of 0.80 for the major bloom season. The sensitivity of algal blooms to rainfall patterns over the 10-year study period suggest that longer-term temporal and spatial shifts in rainfall, such as multi-decadal cycles and the global-warming phenomenon, will also influence the frequency and intensity of algal blooms.

In blackwater river estuaries, a large portion of external carbon, nitrogen, and phosphorus load are combined in complex organic molecules of varying recalcitrance. Determining their lability is essential to establishing the relationship between anthropogenic loads and eutrophication. A method is proposed in which organic C, N, and P are partitioned into labile and refractory forms, based upon first-order decay estimated by biochemical oxygen demand relative to total organic carbon, and C:N and C:P ratios as a function of organic carbon lability. The technique was applied in developing total maximum daily loads for the lower St. Johns, a blackwater Atlantic coastal plain river estuary in Northeast Florida. Point source organic nutrients were determined to be largely labile. Urban runoff was found to have the highest relative labile organic N and P content, followed by agricultural runoff. Natural forest and silviculture runoff were high in refractory organic N and P. Upstream labile C, N, and P loads were controlled by autochthonous production, with 34-50% of summer total labile carbon imported as algal biomass. Differentiation of labile and refractory organic forms suggests that while anthropogenic nutrient enrichment has tripled the total nitrogen load, it has resulted in a 6.7-fold increase in total labile nitrogen load.

In this paper we examine the potential role of light limitation in the regulation of phytoplankton standing crop in Florida’s largest river, the St. Johns. We hypothesized that spatial and temporal patterns in standing crops of phytoplankton are strongly affected by variations in light availability in the mixed layer, particularly as they relate to river basin morphology and changes in water color, which reach high levels in the St. Johns River. This hypothesis was examined within the context of four principal research objectives: (1) Determination of the spatial and temporal patterns of phytoplankton standing crops and key environmental parameters related to nutrient concentration and light extinction, (2) Estimation of spatial and temporal patterns of mean light availability in the mixed-layer, (3) Examination of the correlations between phytoplankton standing crops and light availability, and (4) Evaluation of the relative role of different limiting factors on the regulation of phytoplankton standing crop. The results of this study revealed a relationship between standing crops and light availability. Twelve sampling sites along a 130 km reach of the river were sampled and analyzed for phytoplankton abundance, water chemistry, and light attenuation over a three year period. Our empirical results, along with the outcome of our efforts to model light availability for planktonic production were consistent with our original hypothesis. Temporal variations in color were strongly correlated to variability in phytoplankton standing crops. Spatial trends in standing crop were most readily explained through the effects of changing basin morphology and flushing rates. The results are discussed in the context of the River Continuum Concept and variations on this theme specific to blackwater ecosystems.

The lichen flora of the extreme northeastern corner of the Mojave Desert was investigated during the spring of 2009. Collections were made from five sites on the Beaver Dam Slope in Washington Co., Utah, including the privately owned Lytle Ranch Preserve. We have identified 41 lichen-forming fungal species in 23 genera, including 30 saxicolous, 7 terricolous, and 4 corticolous taxa; including, 16 species recorded from Utah for the first time and 10 new records for the Mojave Desert. This study provides a baseline for documenting the distribution of common and sensitive lichen communities along a transition zone between the Mojave Desert, Great Basin, and Colorado Plateau. Key words: Lichens, floristics, Beaver Dam Slope, Mojave Desert.

The determination of a Total Maximum Daily Load (TMDL) for an impaired waterbody is inherently a quantitative analysis; typically requiring the application of mathematical models to estimate unknown loads, relate loads to target concentrations, and to evaluate implementation strategies to achieve water quality targets. The determination of TMDLs for the Lower St. Johns River is complicated by the hydraulics of the estuary and multiple point and non-point loading sources. The relationship between anthropogenic enrichments and processes impacting nutrient, algal and dissolved oxygen dynamics is further complicated by the blackwater nature of this estuary, as characterized by natural occurrences of low oxygen, low transparency and high primary production. To aid in the evaluation of water quality processes in the estuary and the development of TMDLs, a mathematical model was developed for the Lower St. Johns River estuary using the CE-QUAL-ICM water quality model. The model computes and reports concentrations, mass transport, kinetics transformations, and mass balances for 32 water quality state variables. The three-dimensional hydrodynamics for the application were developed by linking CE-QUAL-ICM with the predictions from the Environmental Fluid Dynamics Code (EFDC), applied to the estuary by the St. Johns River Water Management District (SJRWMD). The SJRWMD developed point and non-point source loadings to the water quality model. Specific modifications were made to ICM to increase its applicability to the Lower St. Johns River. The modifications included the addition of three state variables to address the colored dissolved organic matter of this estuary. The model was applied using data for two years of simulation, from December 1996 to November 1998. Model development and model modifications are discussed. l Department of Civil Engineering, Mississippi State University, Box 9546, Mississippi State, MS 39762; 2 US Army Engineer Research and Development Center, Waterways Experiment Station, 3909 Halls Ferry Road, Vicksburg, MS 39180; 3 St. Johns River Water Management District, P.O. Box 1429 Palatka, FL 32178-1429. James Martin is the primary contact and can be reached at 662-3237194 or imarti n @ en gr.msstate.edu.