Regional nutrient thresholds in wadeable streams of New York State protective of aquatic life

Human influence on the landscape has caused nutrients in surface waters to increase to the point where their presence has substantially altered biological communities. Because this is a nationally recognized problem, the United States Environmental Protection Agency (USEPA) tasked each state, tribe, and territory to adopt numeric nutrient criteria. Here we integrate the concept of ecological thresholds with the derivation of effects-based numeric nutrient criteria. Acceptable levels of risk exceeding predefined biocriteria were determined using conditional probability and nonparametric changepoint analysis. We show how certain community metrics exhibit threshold responses to nutrients. Using these thresholds, we suggest nutrient values protective of aquatic life and characterize community composition. Nutrient criteria were suggested for two aggregations of USEPA's nutrient ecoregions in New York State an upland pristine forested region (Ecoregions VIII and XI) and a nutrient-enriched lowland region (Ecoregions VII and XIV). Of 11 biological community metrics evaluated, 5 had a strong response to nutrients (NBI-P, NBI-N, HBI, TRI, and DMA). Maximum probabilities of exceeding the biological impairment thresholds established for these metrics ranged from 81% to 100%. Changepoint analysis conducted on probability outcomes of these metrics resulted in nutrient thresholds at or above USEPA nutrient guidance values, depending on ecoregion and nutrient variable (Ecoregion VIII/XI: 15 μg/L TP, 472 μg/L TN, 150 μg/L NO₃-N, Ecoregion VII/XIV: 17 μg/L TP, 1133 μg/L TN, 356 μg/L NO₃-N). Results of taxonomic similarity percentages (SIMPER) and species contributions indicate that several orders of macroinvertebrates and diatoms exhibit significant shifts in their percent of contributions to sample similarity in response to changes in nutrient concentrations.     

Nonparametric approaches for estimating regional lake nutrient thresholds

Nonparametric approaches including a classification and regression tree (CART), a nonparametric changepoint analysis (nCPA) and a Bayesian hierarchical modeling (BHM) method were developed to determine ecoregional nutrient response thresholds. A CART analysis revealed that hierarchical structure was important for predicting Chl a concentrations from total nitrogen (TN) and total phosphorus (TP). The nCPA and BHM methods confirmed the CART results for each node in the tree, and the 90% confidence interval for each threshold was calculated to quantify uncertainty. The CART, nCPA, and BHM methods suggested that the nutrient criteria differed significantly within certain nutrient ecoregions and that numerical nutrient criteria of 0.0150–0.222 mg/L TP and 0.300–1.766 mg/L TN may control Chl a concentrations in the various lake ecoregions. The results of this analysis suggest that the integration of CART, nCPA and BHM might be useful for determining nutrient thresholds.     

The threshold responses of phytoplankton community to nutrient gradient in a shallow eutrophic Chinese lake

Excessive nutrient loads resulted in cascading trophic effects and ecosystem responses. Aims of this study were to determine if the thresholds in nutrient gradient related to phytoplankton community composition could be identified in eutrophic lake, and further to analyze the change of phytoplankton assemblage along the nutrient concentration based on Threshold Indicator Taxa ANalysis (TITAN). The results presented the significant community thresholds estimate for negative taxa declining at 1.650 mg/L TN and 131.5 μg/L TP, as well as simultaneously increasing for positive taxa at 1.665 mg/L TN and 151.5 μg/L TP along nutrient enrichment gradient. However, there was unremarkable change point determined for TN:TP ratios in Lake Dianchi. Elevated TN and TP altered the phytoplankton assemblage, even may induce the fade of algal blooms across the threshold in the hypertrophic lake. The findings could provide implications for deeply deciphering abrupt transitions for phytoplankton assemblage and developing nutrient tactics to protect the lake ecosystems.     

Nutrient concentrations in tidal creeks as indicators of the water quality role of mangrove wetlands in Southwest Florida

Coastal mangroves have the potential to improve the water quality of urban and rural runoff before it is discharged into adjacent coastal bays and oceans; but they also can be impaired by excessive pollutants from upstream. Nutrients (phosphorus and nitrogen), salinity, and other water quality parameters were measured in five mangrove tidal creeks in different hydrogeomorphic and urbanization settings during high and low tides over a calendar year of wet (June and August 2015) and dry (February and April 2016) seasons in the Greater Naples Bay area in Southwest Florida, USA. Nutrient concentrations (ave. ± std error) in the tidal creeks were 0.055 ± 0.008 mg-P/L for total phosphorus (TP) and 0.610 ± 0.020 mg-N/L for total nitrogen (TN), with an average N:P ratio of 11.4:1. Average wet season TP (0.075 ± 0.010 mg-P/L) was significantly higher than the dry season TP (0.033 ± 0.003 mg-P/L; p < 0.01, f = 15.17, f_crit = 3.89) and the average wet season TN (0.75 ± 0.03 mg-N/L) was significantly higher than dry season TN (0.52 ± 0.02 mg/L; p < 0.01, f = 64.14, f_crit = 3.89), suggesting that urban stormwater runoff is directly or indirectly affecting the nutrient conditions in these mangroves. Significant differences in nutrient concentrations between low tide and high tide were not found for either TP (p = 0.43, f = .63, f_crit = 3.88) or TN (p = 0.20, f = 1.66, f_crit = 3.89). These differences were confirmed by a PCA and cluster analyses, which found differences to be seasonal. We could not conclude from these results whether these five mangrove wetlands were sources nor sinks of nutrients based simply on the measurement of nutrient concentrations. But we illustrated that nutrient concentrations were indicators of the mangroves’ hydrogeomorphic settings, their tidal fluxes from Naples Bay, and the Bay's upstream watersheds, and less by direct urban runoff.     

Using algal metrics and biomass to evaluate multiple ways of defining concentration-based nutrient criteria in streams and their ecological relevance

We examined the utility of nutrient criteria derived solely from total phosphorus (TP) concentrations in streams (regression models and percentile distributions) and evaluated their ecological relevance to diatom and algal biomass responses. We used a variety of statistics to characterize ecological responses and to develop concentration-based nutrient criteria (derived from ecological effects) for streams in Connecticut, USA, where urbanization is the primary cause of watershed alteration. Mean background TP concentration in the absence of anthropogenic land cover was predicted to be 0.017 mg/l, which was similar to the 25th percentile of all study sites. Increased TP concentrations were significantly correlated with altered diatom community structure, decreased percent low P diatoms and diatoms sensitive to impervious cover, and increased percent high P diatoms, diatoms that increase with greater impervious cover, and chlorophyll a (P < 0.01). Variance partitioning models showed that shared effects of anthropogenic land cover and chemistry (i.e., chemistry affected by land cover) represented the majority of explained variation in diatom metrics and chlorophyll a. Bootstrapped regression trees, threshold indicator taxa analysis, and boosted regression trees identified TP concentrations at which strong responses of diatom metrics and communities occurred, but these values varied among analyses. When considering ecological responses, scientifically defensible and ecologically relevant TP criteria were identified at (1) 0.020 mg/l for designating highest quality streams and restoration targets, above which sensitive taxa steeply declined, tolerant taxa increased, and community structure changed, (2) 0.040 mg/l, at which community level change points began to occur and sensitive diatoms were greatly reduced, (3) 0.065 mg/l, above which most sensitive diatoms were lost and tolerant diatoms steeply increased to their maxima, and (4) 0.082 mg/l, which appeared to be a saturated threshold, beyond which substantially altered community structure was sustained. These criteria can inform anti-degradation policies for high quality streams, discharge permit decisions, and future strategies for watershed development and managment. Our results indicated that management practices and decisions at the watershed scale will likely be important for improving degraded streams and conserving high quality streams. Results also emphasized the importance of incorporating ecological responses and considering the body of evidence from multiple conceptual approaches and statistical analyses for developing nutrient criteria, because solely relying on one approach could lead to misdirected decisions and resources.     

Developing a regional diatom index for assessment and monitoring of freshwater streams in sub-tropical Australia

The use of borrowed indices to assess stream health has limitations and research suggests a need to develop more reliable regionally based indices that are sensitive to the relationship between taxa and environmental conditions. Implementing this is challenging in the Southern Hemisphere given the scarcity of diatom indices, specifically in sub-tropical areas. The purpose of this study was to develop a regionally based diatom index to assess freshwater lotic systems in sub-tropical eastern Australia and compare the results with borrowed indices to derive meaningful inferences on river health. A total of 119 epilithic diatom and water samples were collected during 2014–2015 from the Richmond River Catchment in Northern NSW Australia. Statistical analysis indicated that total phosphorus (TP) and total nitrogen (TN) were strong variables influencing the data set and subsequently TP was chosen as a nutrient proxy for the index. Analysis of diatoms resulted in TP sensitivity values (1–5) being assigned to 105 species with relative abundance of >1% in the data set. These species were used to calculate the Richmond River Diatom Index (RRDI) for 45 sites within the Catchment. The index effectively scored sites along the environmental gradient with sites in the upper catchment generally scoring lower (healthier) than the mid and lower catchment sites. The index compared positively with both the Diatom Species Index for Australian Rivers (DSIAR) (r = 0.76) and the Trophic Diatom Index (TDI) (r = 0.65). Further research is suggested to test the RRDI on independent sites in neighbouring catchments and develop class boundaries from the RRDI so that the index can be readily used by water managers to assess and monitor freshwater systems in sub-tropical Australia.     

Environmental factors controlling colony formation in blooms of the cyanobacteria Microcystis spp. in Lake Taihu,China

Nitrogen (N) and phosphorus (P) over-enrichment has accelerated eutrophication and promoted cyanobacterial blooms worldwide. The colonial bloom-forming cyanobacterial genus Microcystis is covered by sheaths which can protect cells from zooplankton grazing, viral or bacterial attack and other potential negative environmental factors. This provides a competitive advantage over other phytoplankton species. However, the mechanism of Microcystis colony formation is not clear. Here we report the influence of N, P and pH on Microcystis growth and colony formation in field simulation experiments in Lake Taihu (China). N addition to lake water maintained Microcystis colony size, promoted growth of total phytoplankton, and increased Microcystis proportion as part of total phytoplankton biomass. Increases in P did not promote growth but led to smaller colonies, and had no significant impact on the proportion of Microcystis in the community. N and P addition together promoted phytoplankton growth much more than only adding N. TN and TP concentrations lower than about TN 7.75–13.95 mg L⁻¹ and TP 0.41–0.74 mg L⁻¹ mainly promoted the growth of large Microcystis colonies, but higher concentrations than this promoted the formation of single cells. There was a strong inverse relationship between pH and colony size in the N&P treatments suggesting CO₂ limitation may have induced colonies to become smaller. It appears that Microcystis colony formation is an adaptation to provide the organisms adverse conditions such as nutrient deficiencies or CO₂ limitation induced by increased pH level associated with rapidly proliferating blooms.     

A nutrient biotic index (NBI) for use with benthic macroinvertebrate communities

Aquatic macroinvertebrates have been among the principal biological communities used for freshwater monitoring and assessment for several decades, but macroinvertebrate biomonitoring has not incorporated nutrient measures into assessment strategies. Two nutrient biotic indices were developed for benthic macroinvertebrate communities, one for total phosphorus (NBI-P), and one for nitrate (NBI-N). Weighted averaging was used to assess the distributions of 164 macroinvertebrate taxa across TP and NO₃⁻ gradients and to establish nutrient optima and subsequent nutrient tolerance values. Both the NBI-P and NBI-N were correlated with increasing mean TP and NO₃⁻ values (r = 0.68 and r = 0.57, respectively, p < 0.0001). A three-tiered scale of eutrophication for TP and NO₃⁻ (oligotrophic: ≤0.0175 mg/l TP, ≤0.24 mg/l NO₃⁻, mesotrophic: >0.0175 to ≤0.065 mg/l TP, >0.24 to ≤0.98 mg/l NO₃⁻, eutrophic: >0.065 mg/l TP, >0.98 mg/l NO₃⁻) was also established through cluster analysis of invertebrate communities using Bray–Curtis (quantitative) similarity. Significant differences (p < 0.0001) were detected between median NBI-P and NBI-N scores among the three trophic states. Therefore, the nutrient biotic indices (NBIs) appear to accurately reflect changes in stream trophic state. Multimetric water quality assessments were also used to identify thresholds of impairment among the three trophic states. Hodges-Lehman estimation indicated that the greatest change in assessment results occurred between the mesotrophic and eutrophic states. The eutrophic state also represented the highest percentage of overall impairment. Therefore, the suggested threshold for nutrient impairment is the boundary between mesotrophic and eutrophic (0.065 mg/l TP and 0.98 mg/l NO₃⁻). The corresponding NBI-P score (6.1) and NBI-N score (6.0) for this threshold incorporate predictive capabilities into the NBIs. The NBI and index score thresholds of impairment will provide monitoring programs with a robust measure of stream nutrient status and serve as a useful tool in enforcing regional nutrient criteria.     

Diatom biomonitoring of streams: Reliability of reference sites and the response of metrics to environmental variations across temporal scales

Benthic diatoms are widely used indicators of human impacts on stream ecosystems because they are very responsive to changing environmental conditions. However, little research has explicitly focused on their reliability with regards to temporal variation in assemblage structure and environmental conditions. We examined variability in diatom-environment relationships at bi-weekly, monthly, and yearly time scales from 7 reference, 7 agricultural, and 2 acid mine drainage (AMD)-impacted streams, and how nutrient and pH fluctuations may affect the interpretation of diatom metrics and the Diatom Model Affinity (DMA) index. Reference streams had less bi-weekly variability in NO₃-N concentrations than non-reference streams. The % eutraphentic diatoms and DMA scores were more strongly correlated with seasonal means of NO₃-N and PO₄-P concentrations than with same day concentrations. Most nutrient indicator metrics had strong correlations with watershed land use. All 14 non-AMD streams experienced substantial increases in NO₃-N and decreases in temperature from November to May, which were associated with high species turnover, substantial changes in community structure, reduced diversity and richness, increased relative abundances of high nutrient diatoms, and decreases in low nutrient diatoms and DMA scores. The % acidophilic diatoms and DMA scores were significantly correlated with increased pH associated with greater precipitation at AMD sites from December to April (r = ?0.77, r = 0.62, respectively; P < 0.01). Yearly, DMA scores for all reference streams were consistently in the minimally impaired category, whereas scores for non-reference streams varied among impairment categories. Reference sites serve as reliable benchmarks for diatom ecological integrity during the summer. In this region, June to October is a recommended time period for diatom sampling in monitoring programs because subsequent shifts in hydrologic regimes, nutrients, and diatom assemblages occurred, affecting all sites and masking among stream differences attributable to agricultural land uses.     

Kinetics of pollutant removal from domestic wastewater in a tropical horizontal subsurface flow constructed wetland system: Effects of hydraulic loading rate

The treatment capacity of constructed wetlands is expected to be high in tropical areas because of the warm temperatures and the associated higher rates of microbial activity. A pilot scale horizontal subsurface flow constructed wetland system filled with river sand and planted with Phragmites vallatoria (L.) Veldkamp was set up in the southern part of Vietnam to assess the treatment capacity and the removal rate kinetics under tropical conditions. The system received municipal wastewater at four hydraulic loading rates (HLRs) of 31, 62, 104 and 146 mm day^?1. Removals of TSS, BOD₅ and COD were efficient at all HLRs with mean removal rates of 86–95%, 65–83% and 57–84%, respectively. Removals of N and P decreased with HLRs and were: NH₄-N 0–91%; TN 16–84% and TP 72–99%. First-order area-based removal rate constants (k, m year^?1) estimated from sampling along the length of the wetland from inlet to outlet at the four HLRs were in the range of 25–95 (BOD₅), 22–30 (COD), 31–115 (TSS), 5–24 (TN and TKN) and 41–84 (TP) at background concentrations (C*) of 5, 10, 0, 1.5 and 0 mg L^?1, respectively. The estimated k-values should not be used for design purposes, as site-specific differences and stochastic variability can be high. However, the study shows that domestic wastewater can be treated in horizontal subsurface flow constructed wetland systems to meet even the most stringent Vietnamese standards for discharge into surface waters.     

Characteristics of nitrous oxide (N2O) emission from intermittently aerated sequencing batch reactors (IASBRs) treating slaughterhouse wastewater at low temperature

This study investigated the characteristics of nitrous oxide (N₂O) emission from intermittently aerated sequencing batch reactors (IASBRs) treating high strength slaughterhouse wastewater at 11 °C, where partial nitrification followed by denitrification (PND) was achieved. N₂O generation and emission was examined at three aeration rates of 0.4, 0.6, and 0.8 L air/min in three IASBRs (SBR1, SBR2, and SBR3, respectively). The slaughterhouse wastewater contained chemical oxygen demand (COD) of 6057 ± 172.6 mg/L, total nitrogen (TN) of 576 ± 15.1 mg/L, total phosphorus (TP) of 52 ± 2.7 mg/L and suspended solids (SS) of 1843 ± 280.5 g/L. In the pseudo-steady state, the amount of N₂O emission was up to 5.7–11.0% of incoming TN. The aeration rate negatively affected N₂O emission and the ratio of N₂O emission to incoming TN was reduced by 48.2% when the aeration rate was increased from 0.4 to 0.8 L air/min. Results showed that more N₂O was generated in non-aeration periods than in aeration periods. Lower DO concentrations enhanced N₂O generation in the aeration periods (probably via nitrifier denitrification) while low DO concentrations (lower than 0.2 mg/L) did not affect N₂O generation in the non-aeration periods (probably via heterotrophic denitrification). When PHB was utilized as the organic substrate for denitrification, there was a high N₂O generation potential. It was estimated that 1.8 mg N₂O-N was generated accompanying per mg PHB consumed.     

Toward scrubbing the bay: Nutrient removal using small algal turf scrubbers on Chesapeake Bay tributaries

Restoration of the Chesapeake Bay poses significant challenges because of increasing population pressure, conversion of farmland to urban/suburban development, and the expense of infrastructure needed to achieve significant and sustained nutrient reductions from agricultural and urban sources. One radical approach for removing non-point source nutrients before they reach the bay is to deploy large-scale algal turf scrubbers along its tributaries. The objective of this study was to determine rates of nutrient removal and algal fatty acid production using small ATS units located along three Chesapeake Bay rivers. Small-scale ATS units (each containing 1 m² growing area) were operated for 5–10 months from April 2007 to April 2008 on three western shore tributaries of the Chesapeake Bay in Maryland: the Bush River, the Patapsco River and the Patuxent River. Total nitrogen (TN) and total phosphorus (TP) removal rates at the Patuxent site fluctuated considerably but averaged 250 mg TN, 45 mg TP m^?2 day^?1 from May to October 2007, then decreased to 16 mg TN, 3 mg TP m^?2 day^?1 from December 2007 to February 2008. Nutrient removal rates at the Bush river site also fluctuated but averaged only 85 mg TN, 10 mg TP m^?2 day^?1 from May to June 2007, before decreasing to <10 mg TN, <1 mg TP m^?2 day^?1 from July to September 2007. The Patapsco River unit began operation in August 2007, reached its maximum removal values of 150 mg TN, 18 mg TP m^?2 day^?1 from mid-October to late-November 2007, then decreased to values of 45 mg TN, 4 mg TP m^?2 day^?1 from November 15, 2007 to mid-April 2008. In the best case (Patuxent site from May to October 2007), daily removal rates of 250 mg N and 45 mg P m^?2 are equivalent to removal rates of 380 kg N and 70 kg P ha^?1 over a 150-day season in Maryland. Fatty acid (FA) content of the harvested material was consistently low (0.3–0.6% of dry weight) and varied little between sites. Mean algal FA production rates (23–54 mg FA m^?2 day^?1) are equivalent to rates of 34–81 kg FA ha^?1 year^?1 based on a 150-day operational season in Maryland.     

Effects of nutrients on arsenic accumulation by arsenic hyperaccumulator Pteris vittata L.

This research investigated the effects of various nutrients on arsenic (As) removal by arsenic hyperaccumulator Pteris vittata L. in a Hoagland nutrient solution (HNS). The treatments included different concentrations of Ca and K in 20% strength of HNS, different strengths of HNS (10, 20 and 30%), different strengths of HNS (10 and 20%) with and without CaCO₃, and different concentrations of Ca, K, NO₃, NH₄, and P in 20% strength of HNS. The plants were grown in nutrient solution containing 1 mg As L^?1 for 4 weeks except the Ca/K experiment where the plants were grown in nutrient solution containing 10 or 50 mg As L^?1 for 1 week. Adding up to 4 mM Ca or 3 mM K to 20% strength HNS significantly (P < 0.05) increased plant arsenic accumulation when the solution contained 10 mg As L^?1. Plant arsenic removal was reduced with increasing Ca and K concentrations at 50 mg As L^?1. Lower strength of HNS (10%) resulted in the greatest plant arsenic removal (79%) due to lower competition of P with As for plant uptake. Addition of CaCO₃ to 20% strength of HNS significantly increased arsenic removal by P. vittata. Among the nutrients tested, NO₃ and CaCO₃ were beneficial to plant arsenic removal while NH₄, P and Cl had adverse effects. This experiment demonstrated that it is possible to optimize plant arsenic removal by adjusting nutrients in the growth medium.     

Comparing diatom and Alexandrium catenella/tamarense blooms in Thau lagoon: Importance of dissolved organic nitrogen in seasonally N-limited systems

Diatom blooms in Thau lagoon are always related to rain events leading to inputs of inorganic nutrients such as phosphate, ammonium and nitrate through the watershed with time lags of about 1 week. In contrast, blooms of Alexandrium catenella/tamarense can occur following periods of 3 weeks without precipitation and no significant input of conventional nutrients such as nitrate and phosphate. Field results also indicate a significant drop (from 22–25 to 15–16 μM over 3 days) in dissolved organic nitrogen (DON) at the bloom peak, as well as a significant inverse relationship between A. catenella/tamarense cell density and DON concentrations that is not apparent for diatom blooms. Such dinoflagellate blooms are also associated with elevated (6–9 μM) ammonium concentrations, a curious feature also observed by other investigators, possibly the results of ammonium excretion by this organism during urea or other organic nitrogen assimilation.The potential use of DON by this organism represents short cuts in the nitrogen cycle between plants and nutrients and requires a new model for phytoplankton growth that is different from the classical diatom bloom model. In contrast to such diatom blooms that are due to conventional (nitrate, phosphate) nutrient pulses, Alexandrium catenella/tamarense blooms on the monthly time scale are due to organic nutrient enrichment, a feature that allows net growth rates of about 1.3 d⁻¹, a value higher than that generally attributed to such organisms.     

The role of plants in the removal of nutrients at a constructed wetland treating agricultural (dairy) wastewater,Ontario, Canada

The South Nation River Watershed, in eastern Ontario, Canada, is an agricultural watershed impacted by excess nutrient loading primarily from agricultural activities. A constructed wetland for the treatment of agricultural wastewater from a 150-cow dairy operation in this watershed was monitored in its eighth operating season to evaluate the proportion of total nitrogen (TN) (approximated by total Kjeldahl nitrogen (TKN) due to low NO₃⁻) and total phosphorus (TP) removal that could be attributed to storage in Typha latifolia L. and Typha angustifolia L., which dominate this system. Nutrient loading rates were high, with 16.2 kg ha⁻¹ d⁻¹ N and 3.4 kg ha⁻¹ d⁻¹ P entering the wetland and loading the first wetland cell. Plant uptake accounted for 0.7% of TKN removal when the vegetated free water surface cells were considered together. However, separately, in the second wetland cell with lower N and P loading rates, plants accounted for 9% of TKN, 21% of NH₄⁺ and 5% of TP removal. Plant uptake was significant to overall removal given wetland age and nutrient loading. Nutrient storage during the growing season at this constructed wetland helped reduce the nutrient load entering the watershed, already stressed by intensive local agriculture.     

Diatoms as indicators of isolated herbaceous wetland condition in Florida,USA

Benthic, epiphytic, and phytoplanktonic diatoms, as well as soil and water physical–chemical parameters, were sampled from 70 small (average 0.86 ha) isolated depressional herbaceous wetlands located along a gradient of human disturbance in peninsular Florida to (1) compare diatom assemblage structure between algal types; (2) develop biological indicators of wetland condition; (3) examine synecological relationships between diatom structure and environmental variables, with the ultimate goal of developing an index of biological integrity using a single assemblage. Collected diatom samples were enumerated to 250 valves and identified to species or subspecies. An assessment of wetland condition was made using a landscape-scale human disturbance score (Landscape Development Intensity index, LDI), calculated for each site using land use maps and GIS.Assemblages from both impaired and reference sites were compared using blocked multi-response permutation procedures, the percent similarity index, and visually examined using non-metric multidimensional scaling (NMDS). No ecologically significant compositional differences were found within sites. Mantel's test (Mantel's r = 0.29, p < 0.0001) and NMDS (stress: 14.52, variance: 78.5%) identified epiphytic diatoms as the most responsive to human disturbance. Strong significant correlations (|r_s| > 0.50, p < 0.05) were found between epiphytic NMDS site scores and soil pH, specific conductivity, water total phosphorous, and LDI, while soil pH, water color, soil TP, and turbidity were also significantly correlated (p < 0.05).Metrics to assess wetland condition were developed using epiphytic abundance data. Epiphytic taxa sensitive or tolerant to human landscape modification were identified using Indicator Species Analysis, and autecological indices relating diatom sensitivity to nutrients, pH, dissolved oxygen levels, saprobity, salinity, and trophic status were calculated. Fourteen final metrics were identified, scored on an ordinal scale, and combined into the Diatom Index of Wetland Condition (DIWC). The DIWC was highly correlated with the disturbance score (Spearman's r_s = −0.71, p < 0.0001), although the results need to be validated.     

Nutrient removal in wetlands with different macrophyte structures in eastern Lake Taihu,China

A natural wetland of about 12 000 m² along the east coast of Lake Taihu was separated into five subzones with different macrophyte structures to investigate their nutrient removal dynamics. Wastewater was continuously pumped into the wetland from July 2008 to June 2009 at an average rate of 22 m³/h. Neighboring natural wetland with high density of macrophyte was chosen as a comparison site. The removal of TN, TDN, TP, and TDP in the experimental wetlands as a whole was about 79.3, 54.5, 4.5, and 3.4 kg, respectively. The decrease of nitrogen concentration was more pronounced in winter (January–March) 2009, representing a respective reduction of 46.4%, 48.0%, and 47.9% in TN, TDN, and NH₄–N concentration. Results reveal a higher nutrient removal potential in wetland dominated by Typha orientalis Presl, Zizania latifolia Turcz, and Hemarthria sibirica under high nutrient load. However, areas dominated by Zizania latifolia Turcz, Nelumbo nucifera Gaertn, and Ceratophyllum demersum L. had better purification performance when the above-water-surface macrophytes were harvested frequently. Dissolved oxygen, pH, and oxidation–reduction potential decreased with the increase of the percentage of Zizania latifolia Turcz-dominated macrophytes. High nutrient concentration in the comparison site and net increase of NH₄–N in Z1 indicate the possibility of water re-pollution by intense macrophyte decomposition. Furthermore, results suggest that harvesting macrophytes has potential ability in nitrogen, especially ammonium nitrogen removal, and hence could be considered in wetland construction for lake restoration.     

Effects of urban and non-urban land cover on nitrogen and phosphorus runoff to Chesapeake Bay

The aim of this study was to determine the effects of catchment and riparian stream buffer-wide urban and non-urban land cover/land use (LC/LU) on total nitrogen (TN) and total phosphorus (TP) runoff to the Chesapeake Bay. The effects of the composition and configuration of LC/LU patches were explored in particular. A hybrid-statistical-process model, the SPAtially Referenced Regression On Watershed attributes (SPARROW), was calibrated with year 1997 watershed-wide, average annual TN and TP discharges to Chesapeake Bay. Two variables were predicted: (1) yield per unit watershed area and (2) mass delivered to the upper estuary. The 166,534 km² watershed was divided into 2339 catchments averaging 71 km². LC/LU was described using 16 classes applied to both the catchments and also to riparian stream buffers alone. Seven distinct landscape metrics were evaluated. In all, 167 (TN) and 168 (TP) LC/LU class metric combinations were tested in each model calibration run. Runs were made with LC/LU in six fixed riparian buffer widths (31, 62, 125, 250, 500, and 1000 meters (m)) and entire catchments. The significance of the non-point source type (land cover, manure and fertilizer application, and atmospheric deposition) and factors affecting land-to-water delivery (physiographic province and natural or artificial land surfaces) was assessed. The model with a 31 m riparian stream buffer width accounted for the highest variance of mean annual TN (r² = 0.9366) and TP (r² = 0.7503) yield (mass for a specified time normalized by drainage area). TN and TP loadings (mass for a specified time) entering the Chesapeake Bay were estimated to be 1.449 × 10⁸ and 5.367 × 10⁶ kg/yr, respectively. Five of the 167 TN and three of the 168 TP landscape metrics were shown to be significant (p-value ≤ 0.05) either for non-point sources or land-to-water delivery variables. This is the first demonstration of the significance of riparian LC/LU and landscape metrics on water quality simulation in a watershed as large as the Chesapeake Bay. Land cover metrics can therefore be expected to improve the precision of estimated TN and TP annual loadings to the Chesapeake Bay and may also suggest changes in land management that may be beneficial in control of nutrient runoff to the Chesapeake Bay and similar watersheds elsewhere.     

Ecology and distribution of diatoms in Biscayne Bay,Florida (USA): Implications for bioassessment and paleoenvironmental studies

The spatial and temporal distribution of planktonic, sediment-associated and epiphytic diatoms among 58 sites in Biscayne Bay, Florida was examined in order to identify diatom taxa indicative of different salinity and water quality conditions, geographic locations and habitat types. Assessments were made in contrasting wet and dry seasons in order to develop robust assessment models for salinity and water quality for this region. We found that diatom assemblages differed between nearshore and offshore locations, especially during the wet season when salinity and nutrient gradients were steepest. In the dry season, habitat structure was primary determinant of diatom assemblage composition. Among a suite of physicochemical variables, water depth and sediment total phosphorus (STP) were most strongly associated with diatom assemblage composition in the dry season, while salinity and water total phosphorus (TP) were more important in the wet season. We used indicator species analysis (ISA) to identify taxa that were most abundant and frequent at nearshore and offshore locations, in planktonic, epiphytic and benthic habitats and in contrasting salinity and water quality regimes. Because surface water concentrations of salts, total phosphorus, nitrogen (TN) and organic carbon (TOC) are partly controlled by water management in this region, diatom-based models were produced to infer these variables in modern and retrospective assessments of management-driven changes. Weighted averaging (WA) and weighted averaging partial least squares (WA-PLS) regressions produced reliable estimates of salinity, TP, TN and TOC from diatoms (r² = 0.92, 0.77, 0.77 and 0.71, respectively). Because of their sensitivity to salinity, nutrient and TOC concentrations diatom assemblages should be useful in developing protective nutrient criteria for estuaries and coastal waters of Florida.     

Evaluation of phosphorus distribution and bioavailability in sediments of a subtropical wetland reserve in southeast China

The phosphorus (P) fractions and bioavailable P in the sediments from the Quanzhou Bay Estuarine Wetland Nature Reserve were investigated using chemical extraction methods for the first time to study the distribution and bioavailability of P in the reserve sediments. A hypothesis was presented suggesting that the bioavailable P in the sediments could be evaluated using the P fractions. The total phosphorus (TP), inorganic phosphorus (IP), organic phosphorus (OP), non-apatite phosphorus (NAIP), and apatite phosphorus (AP) contents in the sediments were in the ranges of 303.87–761.59 mg kg⁻¹, 201.22–577.66 mg kg⁻¹, 75.83–179.16 mg kg⁻¹, 28.86–277.90 mg kg⁻¹, and 127.36–289.94 mg kg⁻¹, respectively. The water soluble phosphorus (WSP), readily desorbable phosphorus (RDP), algal available phosphorus (AAP), and NaHCO₃ extractable phosphorus (Olsen-P) contents in the sediments were in the ranges of 0.58–357.17 mg kg⁻¹, 80.77–586.75 mg kg⁻¹, 1.09–24.12 mg kg⁻¹, and 54.96–676.82 mg kg⁻¹, respectively. The correlation analysis results showed that the NAIP was the major component of the bioavailable P and that the impact of the AP on the bioavailable phosphorus may be minimal. Due to the low TP content in the sediments of the Quanzhou Bay Estuarine Wetland Nature Reserve, the potential pollution risks of P in the sediments may not be very high. The results also show that the bioavailable P concentrations in the sediments of the Quanzhou Bay Estuarine Wetland Nature Reserve could not be evaluated by measuring the P fractions and that the hypothesis was untenable.