Dynamics of diffuse pollution from US southern watersheds

Forest leaf litter nutrient discharge patterns in snowmelt surface runoff and watershed scale remote sensed simulation

The leaf litter decomposition is the important chain for the nutrient cycle in forest ecosystem, but its degradation dynamics and pulse discharge patterns in freeze-thawing watershed needed complete understanding. By integrating field observations and MODIS data, the temporal-spatial distributions of snow coverage and forest leaf litter biomass were analyzed. The critical period for snowmelt runoff under warming temperature and the relatively slow degradation patterns were identified. The on-site observations snowmelt runoff showed discharge concentration and fraction dynamics of typical forest leaf litter nutrients (carbon, nitrogen, and phosphorus) in thawing period. The snowmelt runoff flow and nutrient flux observed the linear regressions with the increased temperature from -8 °C to 6 °C (r2 = 0.443-0.987). The concentration of TOC, TN, and TP reached summit value around 50.0, 6.0, and 0.5 mg L^-1 in the snowmelt runoff, respectively. The fraction analysis proved that the much high composition of dissolved organic fraction and the biggest organic phosphorus percentage was 94%. The comparison experiments of forest soil with or without leaf litter cover demonstrated that the leaf litter caused a lower discharge load in the snowmelt flow, and the leaf litter cover can decease the potential transport capability of the snowmelt runoff. Coupled with remote sensing data, the watershed leaf litter nutrient discharge model was developed with snowmelt hydrological process mode. The watershed averaged discharge of TOC, TN, and TP from deciduous broad-leaved forest leaf litter was around 851.99, 75.05, and 9.78 mg·m^-2, respectively. The yearly simulation showed the spatial distribution variance of the nutrient discharge loads were held by different forest types, elevations, and slopes. The critical loss area identification provided new mitigations solution. The findings suggested that seasonal discharge of forest leaf litter nutrient in thawing period acted as a key contributor to watershed water pollution.

Lake Nutrient Responses to Integrated Conservation Practices in an Agricultural Watershed

Watershed-scale management efforts to reduce nutrient loads and improve the conservation of lakes in agricultural watersheds require effective integration of a variety of agricultural conservation best management practices (BMPs). This paper documents watershed-scale assessments of the influence of multiple integrated BMPs on oxbow lake nutrient concentrations in a 625-ha watershed of intensive row-crop agricultural activity during a 14-yr monitoring period (1996-2009). A suite of BMPs within fields and at field edges throughout the watershed and enrollment of 87 ha into the Conservation Reserve Program (CRP) were implemented from 1995 to 2006. Total phosphorus (TP), soluble reactive phosphorus (SRP), ammonium, and nitrate were measured approximately biweekly from 1996 to 2009, and total nitrogen (TN) was measured from 2001 to 2009. Decreases in several lake nutrient concentrations occurred after BMP implementation. Reductions in TP lake concentrations were associated with vegetative buffers and rainfall. No consistent patterns of changes in TN or SRP lake concentrations were observed. Reductions in ammonium lake concentrations were associated with conservation tillage and CRP. Reductions in nitrate lake concentrations were associated with vegetative buffers. Watershed simulations conducted with the AnnAGNPS (Annualized Agricultural Non-Point Source) model with and without BMPs also show a clear reduction in TN and TP loads to the lake after the implementation of BMPs. These results provide direct evidence of how watershed-wide BMPs assist in reducing nutrient loading in aquatic ecosystems and promote a more viable and sustainable lake ecosystem.

Using fuzzy logic analysis for siting decisions of infiltration trenches for highway runoff control

Determining optimal locations for best management practices (BMPs), including their field considerations and limitations, plays an important role for effective stormwater management. However, these issues have been often overlooked in modeling studies that focused on downstream water quality benefits. This study illustrates the methodology of locating infiltration trenches at suitable locations from spatial overlay analyses which combine multiple layers that address different aspects of field application into a composite map. Using seven thematic layers for each analysis, fuzzy logic was employed to develop a site suitability map for infiltration trenches, whereas the DRASTIC method was used to produce a groundwater vulnerability map on the island of Oahu, Hawaii, USA. In addition, the analytic hierarchy process (AHP), one of the most popular overlay analyses, was used for comparison to fuzzy logic. The results showed that the AHP and fuzzy logic methods developed significantly different index maps in terms of best locations and suitability scores. Specifically, the AHP method provided a maximum level of site suitability due to its inherent aggregation approach of all input layers in a linear equation. The most eligible areas in locating infiltration trenches were determined from the superposition of the site suitability and groundwater vulnerability maps using the fuzzy AND operator. The resulting map successfully balanced qualification criteria for a low risk of groundwater contamination and the best BMP site selection. The results of the sensitivity analysis showed that the suitability scores were strongly affected by the algorithms embedded in fuzzy logic; therefore, caution is recommended with their use in overlay analysis. Accordingly, this study demonstrates that the fuzzy logic analysis can not only be used to improve spatial decision quality along with other overlay approaches, but also is combined with general water quality models for initial and refined searches for the best locations of BMPs at the sub-basin level.

Hierarchical eco-restoration: a systematical approach to removal of COD and dissolved nutrients from an intensive agricultural area

A systematical approach based on hierarchical eco-restoration system for the simultaneous removal of COD and dissolved nutrients was proposed and applied in a complex residential-cropland area in Kunming, China from August 2006 to August 2008, where the self-purifying capacity of the agricultural ecosystem had been lost. The system includes four main parts: (1) fertilizer management and agricultural structure optimization, (2) nutrients reuse, (3) wastewater treatment, and (4) catchment restoration. The results showed that the average removal efficiencies were 90% for COD, 93% for ammonia, 94% for nitrate and 71% for total dissolved phosphorus (TDP) when the hierarchical eco-restoration agricultural system was in a relatively steady-state condition. The emergence of 14 species of macrophytes and 4 species of zoobenthos indicated that the growth conditions for the plankton were improved. The results demonstrated that this promising and environmentally benign hierarchical eco-restoration system could decrease the output of nutrients and reduce downstream eutrophication risk.

Monitoring of non-point source pollutants load from a mixed forest land use

The aim of this study was to determine the unit load of NPS (non-point source) pollutants including organic variables such as BOD (biochemical oxygen demand), COD (chemical oxygen demand) and DOC (dissolved organic carbon), nitrogen and phosphorus constituents, and suspended solids (SS) and their event mean concentration (EMC) of runoff flows from a water-shed of mixed forest land use by intensive field experiments. Field monitoring for continuous measurements of rainfall, flow, and water quality was conducted over 12 storm events during 2008-2009 using automated and manual sampling methods. The EMCs of individual runoff event were estimated for each water quality constituent based on the flow rate and concentration data of runoff discharge. The average EMCs of BOD, COD, DOC, SS, TN (total nitrogen), NH4(+)-N, NO3(-)-N, TP (total phosphorus), PO4(3-)-P from the mixed forest land were 1.794, 3.498, 1.462, 10.269, 0.862, 0.044, 0.634, 0.034, and 0.005 mg/L, respectively. The annual unit loads of BOD, COD, DOC, SS, TN, NH4(+)-N, NO3(-)-N, TP and PO4(3-)-P were estimated as 66.9, 133.2, 55.5, 429.8, 36.5, 1.6, 26.9, 1.3 and 0.1 kg/(ha x yr), respectively. In addition, affecting parameters on the EMCs were investigated by statistic analysis of the field data. As a result, significant correlations with precipitation, rainfall intensity, and total runoff flows were found in most constituents.

Characterisation of diffuse pollutions from forested watersheds in Japan during storm events - its association with rainfall and watershed features

Forest areas have been identified as important sources of nonpoint pollution in Japan. The managers must estimate stormwater quality and quantities from forested watersheds to develop effective management strategies. Therefore, stormwater runoff loads and concentrations of 10 constituents (total suspended solids, dissolved organic carbon, PO(4)-P, dissolved total phosphorus, total phosphorus, NH(4)-N, NO(2)-N, NO(3)-N, dissolved total nitrogen, and total nitrogen) for 72 events across five regions (Aichi, Kochi, Mie, Nagano, and Tokyo) were characterised. Most loads were significantly and positively correlated with stormwater variables (total event rainfall, event duration, and rainfall intensity), but most discharge-weighted event concentrations (DWECs) showed negative correlations with rainfall intensity. Mean water quality concentration during baseflow was correlated significantly with storm concentrations (r=0.41-0.77). Although all pollutant load equations showed high coefficients of determination (R(2)=0.55-0.80), no models predicted well pollutant concentrations, except those for the three N constituents (R(2)=0.59-0.67). Linear regressions to estimate stormwater concentrations and loads were greatly improved by regional grouping. The lower prediction capability of the concentration models for Mie, compared with the other four regions, indicated that other watershed or storm characteristics should be included in the prediction models. Significant differences among regions were found more frequently in concentrations than in loads for all constituents. Since baseflow conditions implied available pollutant sources for stormwater, the similar spatial characteristics of pollutant concentrations between baseflow and stormflow conditions were an important control for stormwater quality.

Two alternative modes for diffuse pollution control in Wuhan City Zoo

Pollution in urban zoos arises from diffuse and small point sources. However, its control has received little attention in past decades. Online and offline modes of ecological engineering technology were designed to control pollution from small point and diffuse sources in Wuhan City Zoo, China. Their characteristics and performances were investigated in sixteen runoff events from 2003 to 2005. The results showed that the two modes both improved runoff water quality and had high retention rates for water and pollutants. In the outflows, the event mean concentrations (EMCs) of total suspended solids (TSS), chemical oxygen demand (COD), total nitrogen (TN) and total phosphorus (TP) were reduced by 88%, 59%, 46% and 71% for the online mode, and those were 77%, 42%, 50% and 66% for the offline mode. The annual retention rates of pollutant loads for the online mode were 94.9%-98.5% in the three study years; those for the offline mode were 70.5%-86.4%. Based on calculation, the online mode was able to store the runoff of 66.7 mm rainfall completely, and the offline mode could store that of 31.3 mm rainfall. In addition, the online mode can provide an effective way for rainwater utilization and good habitats for aquatic wildlives, and has an excellent aesthetics value for recreationsal pastimes. The offline mode can save land resources and may be an effective and economical measure for diffuse pollution control in urban areas.