4 research outputs found
Modelagem da Lagoa da Pampulha: uma ferramenta para avaliar o impacto da bacia hidrogråfica na dinâmica do fitoplâncton
Characterization of Phosphorus Sources in Rural Watersheds
Correct identification of P sources in rural watersheds is critical for the development of cost-effective measures to combat agriculturally-driven eutrophication. The chemical composition of various storm runoff types (field surface runoff, field drain outfalls, roads, farmyards, and septic tanks) and the receiving streams in three micro (>1 mg Lâ1) than surface and subsurface runoff from cultivated land and pasture (0.02â3.6 mg TP Lâ1, mean 50% vs. <50%) of P in dissolved forms. It is concluded that P sources associated with the functioning of rural communities (impervious surfaces, detergents, and wastewater) may be more ecologically relevant than those associated with agriculture and should be better quantified and controlled to avoid localized eutrophication impacts
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Hydrochemical processes in lowland rivers: insights from in situ, high-resolution monitoring
This paper introduces new insights into the hydrochemical
functioning of lowland river systems using fieldbased
spectrophotometric and electrode technologies. The
streamwater concentrations of nitrogen species and phosphorus fractions were measured at hourly intervals on a continuous basis at two contrasting sites on tributaries of the River Thames â one draining a rural catchment, the River Enborne, and one draining a more urban system, The Cut. The measurements complement those from an existing network of multi-parameter water quality sondes maintained across the Thames catchment and weekly monitoring based on grab samples. The results of the sub-daily monitoring show that streamwater phosphorus concentrations display highly complex dynamics under storm conditions dependent on the antecedent catchment wetness, and that diurnal phosphorus and nitrogen cycles occur under low flow conditions. The diurnal patterns highlight the dominance of sewage inputs in controlling the streamwater phosphorus and nitrogen concentrations at low flows, even at a distance of 7 km from the nearest sewage treatment works in the rural River Enborne. The time of sample collection is important when judging water quality against ecological thresholds or standards. An exhaustion of the supply of phosphorus from diffuse and multiple septic tank sources during storm events was evident and load estimation was not improved by sub-daily monitoring beyond that achieved by daily sampling because of the eventual reduction in the phosphorus mass entering the stream during events. The results highlight the utility of sub-daily water quality measurements and the discussion considers the practicalities and challenges of in situ, sub-daily monitoring
Streamwater phosphorus and nitrogen across a gradient in ruralâagricultural land use intensity
This paper provides an overview of the impacts of rural land use on lowland streamwater phosphorus (P) and nitrogen (N) concentrations and P loads and sources in lowland streams. Based on weekly water quality monitoring, the impacts of agriculture on streamwater P and N hydrochemistry were examined along a gradient of ruralâagricultural land use, by monitoring three sets of âpairedâ (near-adjacent) rural headwater streams, draining catchments which are representative of the major geology, soil types and rural/agricultural land use types of large areas of lowland Britain. The magnitude and timing of P and N inputs were assessed and the load apportionment model (LAM) was applied to quantify âcontinuousâ (point) source and âflow-dependentâ (diffuse) source contributions of P to these headwater streams. The results show that intensive arable farming had only a comparatively small impact on streamwater total phosphorus (TP loads), with highly consistent stream diffuse-source TP yields of ca. 0.5 kg-P/ha/year for the predominantly arable catchments with both clay and loam soils, compared with 0.4 kg-P/ha/year for low agricultural intensity grassland/woodland on similar soil types. In contrast, intensive livestock farming on heavy clay soils resulted in dramatically higher stream diffuse-source TP yields of 2 kg-P/ha/year. The streamwater hydrochemistry of the livestock-dominated catchment
was characterised by high concentrations of organic P, C and N fractions, associated with manure and slurry sources. Across the study sites, the impacts of human settlement were clearly identifiable with effluent inputs from septic tanks and sewage treatment works resulting in large-scale increases in soluble reactive phosphorus (SRP) loads and concentrations. At sites heavily impacted by rural settlements, SRP concentrations under baseflow conditions reached several hundred mg-P/L. Load apportionment
modelling demonstrated significant âpoint-sourceâ P inputs to the streams even where there were no sewage treatment works within the upstream catchment. This indicates that, even in sparsely populated rural headwater catchments, small settlements and even isolated groups of houses are sufficient to cause significant nutrient pollution and that septic tank systems serving these rural communities are actually operating as multiple point sources, rather than a diffuse input