Agricultural non-point source pollution in the Yongding River Basin

More and more nitrogen and phosphorus chemical fertilizers are applied in the upstream of the Yongding River Basin. With the aid of convertibility between emergy and value, the calculated ESI (Environmental Sustainability Index) of basin agricultural production is 0.1056, indicating that local agriculture is seriously unsustainable. According to the different combining types of nitrate and ammonium salts with soil particles, soil nitrogen losses under the influence of rainfall-runoff are quantitatively evaluated from the perspective of the nitrogen cycle. By virtue of the content of dissolved and particulate phosphorus in soil, the calculation process for soil phosphorus loss is modeled according to the field runoff volume. The total nitrogen and total phosphorus losses from soil are 96 kg hm⁻² and 9 kg hm⁻², respectively. The calculation result of nitrogen and phosphorus losses in the basin is certainly reasonable. Finally, the research emphasis of calculation method for reducing basin agricultural non-point source pollution is represented from management level.     

Spatiotemporal modeling of watershed nutrient transport dynamics: Implications for eutrophication abatement

The main objective of this study was to quantify nutrient transport dynamics of a previously ungauged, temperate watershed (145 km²) surrounding a shallow eutrophic lake and discern lake response to external nutrient loading, based on soil water assessment tool (SWAT) and the Organization of Economic Cooperation and Development (OECD) empirical lake models, respectively. A SWAT model was used to simulate baseline nutrient dynamics after its calibration and validation against daily tributary flow, total dissolved phosphorus (TDP), total phosphorus (TP), and nitrate (NO₃) loads. On the watershed scale, median annual TDP, TP, and NO₃ losses were 0.4, 1.1, and 2.0 kg ha^− 1, respectively. The highest median annual TP and NO₃ losses were estimated at 3.7 and 7.7 kg ha^− 1 for pastureland and 1.7 and 3.8 kg ha^− 1 for cropland and mixed forests, respectively. Baseflow was the major nutrient transport pathway over a wide range of precipitation events (450 to 900 mm yr^− 1). Erosion was the predominant surface process exporting P across the watershed. Critical source areas (CSAs) of TP and NO₃ comprised 17% and 4% of the watershed, respectively. Annual mean TP, and mean and maximum chlorophyll content indicated a hyper-eutrophication risk for the lake. An external P load reduction by excess of 80% could be necessary to restore mesotrophy in the lake. Our results suggested that subsurface P transport should not be overlooked a priori when groundwater-dependent and extensively farmed watersheds are managed for eutrophication abatement.     

Development and application of watershed-scale indicator to quantify non-point source P losses in semi-humid and semi-arid watershed,China

Quantifying non-point source (NPS) phosphorus (P) pollution loads is essential for watershed nutrients management. This study intended to develop a NPS P indicator which (1) was suitable in semi-humid and semi-arid watersheds of Northern China; (2) integrated the key NPS P loss factors and constructed them in a simple and physically understandable way and (3) kept P loss forms distinctively separate. An inverse distance-based delivery ratio was proposed to count for the P delivery efficiency from source to watercourses. We applied this P indicator in Luan River Watershed (LRW) of northern China under typical hydrological years and seasons. Results demonstrated that this NPS P indicator predicted reasonable NPS TP loads using simple methods and readily obtainable inputs. The sub-watersheds located in the south of LRW were recognized as the high risk areas of NPS P loss to Panjiakou reservoir. The upland and paddy fields near the river channels were particularly posing high risk and thus should be treated with prioritized management practices such as soil conservation and recommended fertilization. Rainfall-runoff related variables rather than P source variables explained more of the spatial variation in NPS P load and percentages. Using this tool could give policy makers insight into the component and location of NPS P pollution that needs to be the focus of policy at watershed scales before sophisticated studies were conducted in smaller scales.     

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.     

Phosphorus reduction from agricultural runoff in a pilot-scale surface-flow constructed wetland

Excess P in surface waters in Quebec is the primary cause of water quality deterioration and the majority of it is coming from agricultural land as non-point source pollution. The objective of this study was to compare how two substrates, a sandy clay loam and a sand soil, influenced P retention in a surface-flow constructed wetland (CW). A secondary objective was to determine if the hydraulic residence time of the wetland differed between soil types. Measurements were taken at a pilot-scale CW site between July 5 and October 1, 2007. Three cylindrical tank replicates filled with sandy clay loam soil, and three with a sandy soil were planted with cattails (Typha latifolia L.) and reed canary grass (Phalaris arundinaceae L.). The tanks were flooded continuously with an artificial agricultural runoff solution containing 0.3 mg L^?1 dissolved reactive P. The six treatment tanks retained 0.9–1.6 g P m^?2, which corresponded to an average removal efficiency of 41%; there was no significant difference in the P retention by the two soil types. A bromide tracer test revealed a mean hydraulic retention time of 2.2 days for all tanks; however, the active volume of the sand tanks was greater. This investigation suggests that a sandy soil may be less prone to reducing conditions in a surface-flow CW and therefore maintain its role as a P sink for longer than the sandy clay loam.     

Assessment of wind and water erosion risk in the watershed of the Ningxia-Inner Mongolia Reach of the Yellow River,China

The watershed of the Ningxia-Inner Mongolia Reach of the Yellow River (NIMRYR) suffers from soil erosion by wind and water because of the wide distribution of deserts and arsenic sandstones in this region. The sediment generated by erosion fed into the Yellow River directly or by its tributaries, silting up the Yellow River and raising the elevation of the river bed. The silting of the Yellow River result in serious flood disasters in this watershed. Therefore, it is urgent to implement soil conservation projects to control wind and water soil erosion. To reach this objective, understanding the spatial and temporal variations of soil erosion in this watershed is very important. In this study, an assessment of soil erosion risk by wind and water was performed based on soil erosion models. The Integrated Wind Erosion Modeling System (IWEMS) and the Revised Wind Erosion Equation (RWEQ) were used to estimate the wind erosion modulus in this watershed, and the water erosion modulus was estimated by the Revised Universal Soil Loss Equation (RUSLE). The results show that during 2000s, the wind erosion modulus ranged from 0 to 31,440.4 t/km²/a, and the water erosion modulus was from 0 to 24,048.5 t/km²/a. Moreover, the total soil erosion modulus by wind and water has ranged from 0 to 32,792.7 t/km²/a. Due to the influence of regional weather and geomorphology, occurrences of wind and water erosion in this watershed are not identical in their spatial and temporal patterns. Based on the calculated soil erosion modulus, soil erosion risk was assessed according to the “Classification criteria for soil-erosion intensities” (SL190-2007). It was assumed that the areas with erosion intensity higher than slight were at risk of erosion; by this criterion, more than 34% of the total area of the watershed of the NIMRYR would be at erosion risk. Based on this estimation, it was also found that the NIMRYR watershed is not a region of wind–water erosion crisscross and that land-use conversions have a significant impact on soil erosion.     

Whole-system phosphorus balances as a practical tool for lake management

Controlling phosphorus (P) inputs to lakes remains a priority of lake management. This study develops watershed P balances for 11 recreational lakes in Minnesota. Areal P input rates to the watersheds ranged from 0.32 to 6.0 kg P ha⁻¹ year⁻¹ and was linearly related to the percentage of watershed in agriculture. Watershed P retention ranged from 10% to 89% of input P. Although many best management practices work to increase P retention (by trapping P in basins; reducing erosion; filtration), P retention is not sustainable indefinitely, particularly in “hot spots” such as septic leach fields and heavily manured fields. The watershed P balance tool is a framework that can allow watershed managers to develop novel strategies for managing P. P management strategies should be developed to keep P inputs and exports in balance so that P does not accumulate; long-term P accumulation is not sustainable and can eventually lead to lake eutrophication.     

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.     

Long-term phosphorus and nitrogen removal processes and preferential flow paths in Northern constructed peatlands

Four treatment peatlands were studied in Northern Finland in order to determine peat P, Al and Fe concentration distributions and to find removal parameters for nutrient modelling. The sites had been under loading for 10–16 years. About 20 peat samples for analyses of oxalate-extractable and total P, Al and Fe were collected from the depth 0–10 cm in each peatland. The peat P concentration ranged from 0.097 mg g^?1 to 14 mg g^?1 being 1.7 mg g^?1on average. P accumulated in preferential flow path areas. Although P concentrations were locally high, DSSP (the index of potential soil P release from peat to water) was very low in all studied peatlands, indicating that peat was not saturated by phosphorus. The results indicate that Al-based precipitation chemicals increase substantially P retention capacity of peatland and maintain a stabile P reduction in spite of varying P loads. The results also show long-term phosphorus accumulation in peatlands polishing municipal wastewater from activated sludge treatment. The regression analyses showed that k-value for N removal depends on N loading and hydraulic loading. The first-order area model together with regression analysis of the rate constant result in a good agreement between observed and calculated nitrogen concentration. The NH₄-N loading to the peatland should be below 0.10 mg m² d^?1 in order to achieve a high reduction of 70%.     

Phosphorus budget in the Marne Watershed (France): urban vs. diffuse sources,dissolved vs. particulate forms

We evaluated the P sources (point, diffuse), through a nested watershed approach investigating the Blaise (607 km²), dominated by livestock farming, the Grand Morin (1202 km²), dominated by crop farming, and the Marne (12,762 km²), influenced by both agriculture and urbanization. Fertilizers account for the main P inputs (>60%) to the soils. An agricultural P surplus (0.5–8 kg P ha^–1 year^–1) contributes to P enrichment of the soil. The downstream urbanized zone is dominated by point sources (60%, mainly in dissolved forms), whereas in the upstream basin diffuse sources dominate (60%, mostly particulate). Among the diffuse sources (losses by forests, drainage and runoff), losses by runoff clearly dominate (>90%). P retention in the alluvial plain and the reservoir represents 15–30% of the total P inputs. Dissolved and particulate P fluxes at the outlet of the Marne are similar (340 and 319 tons of P year^–1, respectively). The Blaise sub-basin receives P from point and diffuse sources in equal proportions, and retention is negligible. The Grand-Morin sub-basin, influenced by the urbanized zone receives, as does to the whole Marne basin, 60% of P inputs as point sources. The total particulate phosphorus in suspended sediments averaged 1.28 g P kg^–1, of which about 60% are inorganic and 40% organic P. Particulate phosphorus exchangeable in 1 week and 1 year (³²P isotopic method) accounts for between almost 26% and 54% of the particulate inorganic phosphorus in the suspended sediment and might represent an important source of dissolved P, possibly directly assimilated by the vegetation.     

Nitrogen and phosphorus concentrations and export for the upper Kuparuk River on the North Slope of Alaska in 1980

Nitrogen and phosphorus concentrations were measured from May to August 1980 in the upper Kuparuk River, a tundra stream on the North Slope of Alaska. Mean values for nitrogen were 10.8 μg N 1⁻¹ for ammonium, 21.4 μg N 1⁻¹ for nitrate plus nitrite and 248 μg N 1⁻¹ for dissolved organic nitrogen. Mean values for phosphorus were 8.1 μg P 1⁻¹ for total dissolved phosphorus and 4.7 μg P 1⁻¹ for fine particulate phosphorus. Nitrate concentrations were inversely correlated with flow whereas particulate phosphorus concentrations increased during high flows. Export of nitrogen and phosphorus from the watershed during 1980 was estimated to be 4.69, 3.25 and 91 kg km⁻² yr⁻¹ for NO₃-N, NH₄-N and DON-N, respectively, and 2.86 and 3.03 kg km⁻² yr⁻¹ for TDP-P and PP-P. Both the relative concentrations of N and P and the relative amounts exported suggest that phosphorus is in short supply but both nutrients are present in low concentrations comparable to those found previously in tundra ponds at Point Barrow, Alaska.     

Simulation of land use–soil interactive effects on water and sediment yields at watershed scale

Influences of vegetation management on soil erosion have been extensively studied. However, interactive effects between land use and soil are poorly documented in literature. Given the importance of understanding such effects for successful watershed management, the objective of this study was to examine the land use–soil interactive effects on water and sediment yields for the 117,845-ha drainage area upstream of the U.S. Geological Survey flow gauging station 08101000 in the Cowhouse Creek watershed located in north central Texas. The examination was implemented using the Soil and Water Assessment Tool (SWAT), a distributed watershed model that has been widely used to tackle problems relevant to nonpoint source pollution. A SWAT model was calibrated and validated in accordance with the observed daily streamflows at this gauging station. Subsequently, the calibrated model was used to examine changes of water and sediment yields as a result of the conversion of range brush to range grasses on an individual soil basis. The results indicated that for the study area, the removal of range brush would result in an annual water yield increase of 24 mm ha^?1 treated area. However, the removal on an upland soil with a moderately high permeability was predicted to increase the annual water yield by 80 mm ha^?1 treated area, while it would result in a small increase of annual sediment loading (4.2 t ha^?1 treated area) and a minimal alteration to the existing spatial patterns of sediment sources. The increase of water yield would be larger for the removal of range brush on a soil that is adjacent to the stream channels. For a given soil, the predicted water yield increase was greater for the wetter hydrologic condition than that for the drier one. A reasonable generalization of this study was that the development of best management practices for watershed health and sustainability may need to take into account land use–soil interactive effects on an individual soil basis.     

Beef cattle pasture to wetland reconversion: Impact on soil organic carbon and phosphorus dynamics

There is a major need to understand the historical condition and chemical/biological functions of the ecosystems following a conversion of wetlands to agricultural functions. To better understand the dynamics of soil total organic carbon (TOC) and phosphorus (P) during beef cattle pastures to wetland reconversion, soil core samples were collected from the beef cattle pasture and from the natural wetland at Plant City, FL, during five summer seasons (2002–2007). The levels of TOC and soil P were significantly affected by changing land use and hydrology. Draining natural wetlands to grazed pastures resulted in very pronounced reduction of TOC from 180.1 to 5.4 g g^?1. Cumulative concentrations of total phosphorus (TP) in soils (1134 mg kg^?1) under drained condition are two to three times lower than those in soils (2752 mg kg^?1) under flooded condition over the periods of land use reconversion. There was a declining trend (r = 0.82**; p ≤ 0.01) in total soil P from natural wetland (763 mg kg^?1) to altered pastures (340 mg kg^?1), largely as organic-bound P (natural wetland, 48%; grazed pastures, 44%; altered pastures, 29%). These results are important in establishing baseline information on soil properties in pasture and wetland prior to restoring and reconverting pasture back to wetland conditions. The results further suggest that changes in soil properties due to changing land use and hydrologic conditions (drying and re-wetting) could be long lasting.     

Shade tree cover criteria for non-point source pollution control in the Rainforest Alliance coffee certification program: A snapshot assessment of Costa Rica's Tarrazú coffee region

Management of non-point source pollution is of great importance in the context of coffee agriculture, as this land use often coincides with headwater streams that influence water quality at the basin scale. Sustainability certification programs, such as the Rainforest Alliance (RA), provide management guidelines that promote non-point source pollution control in coffee. One of these practices is the maintenance of shade trees within farms, required by RA at a minimum of 40% shade tree cover. Here we assess the effectiveness of this practice in Tarrazú, a high elevation coffee growing region in Costa Rica. We monitored indicators of non-point source pollution in streams with both high and low shade tree cover. Streams with High Shade Tree Cover (HSTC, N = 5 subwatersheds) had 35–55% cover, approximating or exceeding the RA recommendation of at least 40%; and streams with Low Shade Tree Cover (LSTC, N = 5 subwatersheds), had 18–31% cover. We monitored the ten study streams during the dry (April & December), transition (July), and peak (October) rainfall seasons of 2013, and compared responses using t-tests. We found support for the effectiveness of shade tree cover in controlling non-point source pollution: HSTC streams had significantly (p = 0.042) lower mean annual turbidity and significantly (p = 0.004) lower turbidity during the transition season. HSTC streams also had significantly (p = 0.05) lower conductivity values during the transition period, although this trend was weaker through the year. Subwatersheds with HSTC streams were characterized by a higher percentage of RA-certified coffee than LSTC streams. Our study provides evidence of the benefits of RA shade tree cover criteria for managing water quality within high elevation tropical agro-ecosystems, especially if implemented at the watershed scale. These results contribute to our understanding of the role of agroforestry certification on tropical ecosystem conservation, and are the first account of the effectiveness of a specific coffee certification guideline on non-point source pollution control.     

Chemical characteristics of soils and pore waters of three wetland sites dominated by Phragmites australis: relation to vegetation composition and reed performance

Chemical characteristics of soils and soil pore waters, plant species composition and horizontal stand structure were investigated for three reed stands in the Třeboň Basin (Czech Republic): Branná sand pit and two littoral stands of Rožmberk fishpond (Rožmberk East and Rožmberk West). Phragmites stands were expanding, stable and retreating at the three sites, respectively. The elemental soil composition (especially of C, N, P, and K) indicated the lowest trophic conditions at Branná, intermediate at Rožmberk East and the highest at Rožmberk West. This corresponded well also with concentrations of ammonium nitrogen, dissolved reactive phosphate and total phosphorus in the soil pore water. In contrast, Branná had by far the highest level of total nitrogen, determined by nitrate nitrogen (20 mg l⁻¹), and the highest level of total dissolved solids (concentrations of NO₃⁻, SO₄²⁻, Ca²⁺ and Mg²⁺) of all three sites. No conspicuous differences were found among the three stands in biomass and its allocation. The vegetation composition corresponded more closely to elemental soil composition than to total nitrogen or total dissolved solids in the pore water. It is concluded that Branná provides an example of a site subjected to an initiating but dramatic and fast eutrophication while conditions at the two Rožmberk sites indicate a slower but longer lasting eutrophication. Owing to continuous heavy organic loading, Rožmberk West represents a hypertrophic site characterised by the highest levels of organic matter and associated characteristics (soil C, N, P, K, dissolved P), but also by the most severe lack of oxygen of the three sites.     

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.     

Development of a diatom index of biotic integrity for acid mine drainage impacted streams

Acid mine drainage (AMD) resulting from extensive coal mining throughout Appalachia since the 1800s has caused a legacy of severe acid and dissolved metal loads to thousands of stream miles, which has critically impacted aquatic life and ecological attributes. Relationships of diatoms and macroinvertebrates with AMD have been established, but no index specifically designed to quantify AMD impacts using diatoms has been created, nor have the response of multiple organism groups been compared for their utility as indices assessing AMD severity.For the purpose of developing an effective assessment and management strategy for AMD impacted streams, this study created and tested a multi-metric AMD-diatom index of biotic integrity (AMD-DIBI) and compared its response to AMD severity with an already established multi-metric macroinvertebrate community index (ICI). In 2006, 41 sites in southeast Ohio were sampled that represented an AMD impact gradient and non-AMD impacted reference sites. Metrics comprising the AMD-DIBI were selected based on their responsiveness to AMD and nutrient impacts. In the following year, the AMD-DIBI and its metrics were tested on a validation dataset consisting of 18 sites in an AMD impacted watershed. Results indicated a significant correlation between AMD-DIBI and ICI scores, and both indices and all metrics were strongly correlated with water chemistry variables indicative of AMD pollution (P < 0.05). Stepwise multiple regression selected alkalinity and conductivity as most influential to AMD-DIBI (adjusted r² = 0.70) and ICI scores (adjusted r² = 0.66). Narrative classes (e.g., Poor, Fair, Good, and Excellent) defined by index scores provided effective classifications of AMD severity. When tested on the watershed scale, AMD-DIBI and its metrics very successfully quantified AMD gradients and coal mining impacts as indicated by canonical correspondence analysis. This newly developed AMD-DIBI will be very useful for assessing impairment, sensitivity, and recovery of diatom communities in streams damaged or threatened by coal mining activities. In addition, because the AMD-DIBI was very responsive to a gradient of AMD pollution, it could be used in future studies measuring the long-term status of streams and effectiveness of various remediation methods. This study highlights the responsive power of diatom-based metrics.     

Management scenario evaluation for a large treatment wetland using a spatio-temporal phosphorus transport and cycling model

This paper describes the development of a two-dimensional, spatially distributed model to simulate coupled hydrologic and phosphorus (P) biogeochemical processes in a 147-ha cell of a 1544-ha stormwater treatment wetland designed to help protect the greater Everglades, FL, USA. The model was used to assess the effects of a suite of feasible management alternatives on the long-term ability of the wetland to sustain total P (TP) removal. The spatial and temporal dynamics of TP retention were simulated under historical (1995–2000) conditions, and under assumptions of removal of short-circuiting channels and ditches, changes in external hydraulic and TP loading, and long-term (>20 years) impacts on soil and water column TP dynamics under current and reduced load conditions. Internal hydrology and transport processes were calibrated against measured tracer concentrations, and subsequently validated against outflow discharge and spatial chloride concentration data. Cycling of P was simulated as first-order uptake and release, with different uptake coefficients for open water/sparse submerged aquatic vegetation (SAV) areas (0.2 day^?1) and dense SAV areas (0.4 day^?1), and a much lower, uniform release coefficient (1.97 × 10^?4 day^?1). The calibration and validation of the P model showed good agreement with field measurements of water column TP concentrations measured at the wetland outlet (calibration RMSE = 10.5 μg L^?1; validation RMSE = 15.6 μg L^?1). Under simulated conditions of preferential channels eliminated, average annual TP treatment effectiveness increased by 25%. When inflow TP loads were assumed to be eliminated after 6 years of loading, the release of accumulated soil P sustained predicted annual average outlet concentrations above 6.7 μg L^?1 for 18 years, decreasing at a rate of 0.16 μg L^?1 yr^?1. Sensitivity analyses indicate that the most critical model input factors include flow resistance parameters, initial soil TP content, and P cycling parameters compared to initial water level, initial TP concentration in water column, ET and transport parameters.     

Increasing nitrogen depositions can reduce lichen viability and limit winter food for an endangered Chinese monkey

Increasing economic growth and industrial development in China is starting to impact even remote areas such as the Shennongjia nature reserve, where nitrogen pollution is becoming a major environmental threat. The epiphytic lichen flora is particularly rich in this area and is one of the components of this habitat most sensitive to nitrogen pollution. Since lichens represent an important food resource for the endangered monkey species Rhinopithecus roxellana, a reduction in lichen availability would have harmful consequences for the conservation of its habitat in the Shennongjia Mountains. To investigate the effects of increased nitrogen availability on the local lichen communities, so far scarcely considered, we conducted a one-year field experiment measuring growth, survival, and phosphomonoesterase activity of the widespread species Usnea luridorufa in response to nitrogen (up to 50 kg N ha⁻¹ year⁻¹ deposition) and phosphorus supply. Growth and survival of thalli and propagules of U. luridorufa decreased when treated with N deposition >12.05 kg N ha⁻¹ year⁻¹ and >2.14 kg N ha⁻¹ year⁻¹, respectively. The important role of phosphorus availability in relation to nitrogen supply was demonstrated by the increase in phosphomonoesterase activity with increasing nitrogen availability until a nitrogen toxicity threshold was reached. However, the high concentration of phosphorus in rainwater showed that phosphorus is not a limiting nutrient in the area.The results make a contribution to the knowledge of the negative effects of increased N deposition in the Shennongjia forest ecosystem.     

Development of dual fish multi-metric indices of biological condition for streams with characteristic thermal gradients and low species richness

Biological indicators based on fish assemblage characteristics are used to assess stream condition worldwide. Fish-based bioassessment poses challenges in Southern New England, the USA, due to the effects of within-watershed thermal gradients on fish assemblage types, low regional species richness, and lack of minimally disturbed sites. Dual multi-metric indices (MMI) of biological condition were developed for wadeable streams based on fish assemblage characteristics sampled across watershed landscapes with varying levels of human disturbance. A coldwater MMI was developed using streams with drainage area of ≤15 km², and a mixed-water MMI for streams with drainage areas of >15 km². For each MMI development, candidate metrics represented by ecological classes were sequentially tested by metric range, within-year precision, correlation with stream size, responsiveness to landscape-level human disturbances, and redundancy. Resultant coldwater and mixed-water MMI were composed of 5 and 7 metrics, respectively. Stream sites tended to score similarly when the two MMI were applied to transitional sites, i.e., drainage areas of 5–40 km². However, some sites received high scores from the mixed-water MMI and intermediate scores from the coldwater MMI. It was thus difficult to ascertain high-quality mixed-water streams from potential coldwater streams which currently support mixed-water assemblages due to ecological degradation. High-quality coldwater streams were restricted to stream sites with drainage areas ≤15 km². The newly developed fish-based MMI will serve as a useful management tool and the dual-MMI development approach may be applicable to other regions with thermal gradients that transition from coldwater to warmwater within watersheds.