Stream restoration efforts have aimed at increasing hydraulic residence time (HRT) and transient storage (TS) to enhance nutrient uptake, but there have been few controlled studies quantifying HRT and TS influences on nutrient uptake dynamics. We assessed the effects of HRT and TS on ammonium (NH4+) and phosphate (PO43−) uptake through controlled experiments in an artificial channel draining a pristine tropical stream. We experimentally dammed the channel with artificial weirs, to progressively increase HRT, and performed NH4+ and PO43− additions to estimate uptake each time a weir was added. We also ran consecutive additions of NH4+ and PO43− with no weirs, to evaluate short‐term changes in uptake metrics. Also, NH4+ was injected alone to assess potential nitrification. We observed that NH4+ and PO43− uptake rates were much greater in the very first addition, probably due to luxury uptake. The weirs increased mean HRT (from 8.5 to 12 min) and depth (from 6.5 to 8.9 cm) and decreased mean water velocity (0.40–0.28 m s−1). Surprisingly, damming decreased the relative size of transient storage zone (storage zone area/channel area, As/A from 0.72 to 0.55), indicating that greater depth increased A, but not As. Greater HRT increased uptake rates and velocities of both nutrients (p < 0.05). The NH4+ conversion to NO3− was estimated at 18% of NH4+ consumption, indicating that joint additions to measure NH4+ and NO3− uptake would not be feasible in this system. Our results suggest that increases in HRT can lead to a greater short‐term retention of nutrients, with implications for stream management and restoration initiatives.
Artigo recebido em 5 de maio de 2014, versão final aceita em 4 de novembro de 2014. RESUMO:A aplicação de instrumentos econômicos na gestão das águas tem como princípio incentivar a forma racional dos padrões de consumo do bem. Nesta linha a Política Nacional dos Recursos Hídricos, na busca de atribuir um valor econômico à água, introduziu a cobrança pelo uso dela nas Bacias Hidrográficas (BCH) no Brasil. Esta revisão metodológica apresenta as metodologias de cobrança pelo uso da água atualmente empregadas em águas de domínio da União, bem como a arrecadação gerada e os investimentos realizados nas respectivas BCH. No Brasil, o instrumento é empregado nas BCH do Rio Paraíba do Sul, dos rios Piracicaba, Capivari e Jundiaí, do Rio São Francisco e do Rio Doce. Também no Estado do Ceará, pioneiro no país, a cobrança é aplicada pelo uso da água, porém conceitualmente diferenciada. Verificou-se que em todas as BCH de águas com domínio da União, o modelo de cobrança segue a mesma estruturação, considerando todos os tipos de usos de água, principalmente a captação, o consumo e o lançamento de efluentes. Ainda, cada parcela considera os volumes utilizados, o preço unitário pelo uso, os coeficientes próprios e relativos à gestão da BCH. Por outro lado, a cobrança pelo uso da água bruta no Estado do Ceará apresenta-se baseada no atual sistema de tarifação e é definida somente com base na água consumida. A arrecadação setorial apresentou-se variável, no entanto, pode-se citar como setores com maior potencial de arrecadação, o de saneamento básico e o industrial. Ainda, verificou-se que os investimentos realizados com recursos obtidos com a cobrança vêm sendo aplicados, em sua maioria, a ações estruturais que envolvem a recuperação dos recursos hídricos, tais como estações de tratamento e redes de coleta e afastamento de efluentes.Palavras-chave: gestão de recursos hídricos; cobrança pelo uso da água; metodologias de cobrança.ABSTRACT: The purpose of using economic tools in water management is to encourage reasonable water consumption patterns. In this context, the National Water Resources Policy, in order to put an economic price to water, introduced the water pricing in national Watersheds. This methodology review presents the methods for putting a price on water currently used in waters under federal jurisdiction, the generated revenues and investments
This study used multivariate techniques for data analysis in order to determine the natural and anthropogenic factors that contribute to the spatial and temporal variations of water quality in urban watersheds of Caxias do Sul, Brazil. Principal Component Analysis (PCA) was used to analyze data collected at 30 points between September 2012 and January 2014. Monitoring was conducted bimonthly in six urban basins, where a total of 21 physical, chemical and biological parameters were analyzed. We found that PCA can explain 71.3% of the total variance in water quality, and that domestic and industrial pollution are the main Qualidade da água superficial por meio de análise … Rev. Ambient. Água vol. 10 n. 4 Taubaté-Oct. / Dec. 2015 contributors to the water quality variation in the region, especially from the galvanic manufacturing sector. Furthermore, we observed a trend of self-attenuation of pollutants in water downstream from urban areas and great anthropogenic influence as the pressure from urbanized areas decreases.
Pollution abatement through phosphorus and nitrogen retention is a key ecosystem service provided by streams. Human activities have been changing in-stream nutrient concentrations, thereby altering lotic ecosystem functioning, especially in developing countries. We estimated nutrient uptake metrics (ambient uptake length, areal uptake rate, and uptake velocity) for nitrate (NO3–N), ammonium (NH4–N), and soluble reactive phosphorus (SRP) in four tropical Cerrado headwater streams during 2017, through whole-stream nutrient addition experiments. According to multiple regression models, ambient SRP concentration was an important explanatory variable of nutrient uptake. Further, best models included ambient NO3–N and water velocity (for NO3–N uptake metrics), dissolved oxygen (DO) and canopy cover (for NH4–N); and DO, discharge, water velocity, and temperature (for SRP). The best kinetic models describing nutrient uptake were efficiency-loss (R2 from 0.47–0.88) and first-order models (R2 from 0.60–0.85). NO3–N, NH4–N, and SRP uptake in these streams seemed coupled as a result of complex interactions of biotic P limitation, abiotic P cycling processes, and the preferential uptake of NH4–N among N-forms. Global change effects on these tropical streams, such as temperature increase and nutrient enrichment due to urban and agricultural expansion, may have adverse and partially unpredictable impacts on whole-stream nutrient processing.
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