Limnologists and stream ecologists acknowledge the fundamental importance of temperature for regulating many ecological, biological, chemical, and physical processes. I investigated how water temperatures were affected by hydrologic linkages between streams and lakes at various positions along surface water networks throughout several headwater basins in the Sawtooth and White Cloud Mountains of Idaho (USA). Temperatures of streams and lakes were measured for up to 27 months in seven 6 – 41 km2 watersheds, with a range of lake influence. When they were ice-free, warming in lakes resulted in dramatically warmer temperatures at lake outflows compared to inflow streams (midsummer average 6.4°C warming, but as much as 12.5°C). Temperatures cooled as water traveled downstream from lakes, as rapidly as 9°C km-1. Longitudinal stream cooling was usually not strong enough, however, to reduce temperatures to baseline conditions. In early spring, lakes had the opposite effect on streams, as they released water from beneath the ice at near 0°C. Early spring stream water warmed as it flowed downstream from lakes, influenced by additional groundwater inflows. In addition to lakes, other watershed characteristics influenced temperatures, though effects differed seasonally. Multiple regression analyses indicated that lake size, distance from nearest upstream lake, and stream shading were most important in explaining stream temperatures, but the relative importance of each variable changed seasonally.

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Este trabalho teve como objetivo estudar o comportamento espaço-temporal das variáveis limnológicas, no Ribeirão Bonito (SP) a fim de avaliar a descontinuidade ocasionada pelas fontes poluidoras e o processo de autodepuração. Para tanto, foram determinadas variáveis físico-químicas, biológicas, climatológicas e hidrológicas, no eixo longitudinal do rio e utilizado como ferramenta para diferentes cenários de simulações das concentrações de oxigênio dissolvido, o modelo QUAL2E. Foi possível observar, que muitas das variáveis limnológicas estudadas no Ribeirão Bonito sofrem \"descontinuidades\" devido à entrada de esgoto. As concentrações de oxigênio dissolvido têm um gradiente positivo da nascente até a estação 4, sofrendo uma descontinuidade após a estação 6 onde detecta-se o primeiro lançamento de esgoto. O comportamento dessa variável após a entrada de esgoto foi distinto nos dois períodos estudados. As análises de \"Cluster\" e PCA (Análise dos Componentes Principais), realizadas com as médias das variáveis limnológicas, distinguiram diferentes grupos no perfil longitudinal do ribeirão Bonito. Essa distinção pode ser atribuída às já citadas entradas de efluentes e também em decorrência da presença do tributário do Curtume. Pode-se constatar que mesmo com o auxílio natural do processo de autodepuração, muitas das variáveis estudadas não se enquadram aos padrões do corpo receptor conforme previsto pela resolução número 20/86 do CONAMA, sugerindo assim, neste trabalho, um grau de tratamento dos efluentes para que estes padrões sejam respeitados. / The objective of the present paper is to study the spatial-temporal behaviour of the limnological variables, in Bonito stream (SP), in order to evaluate the discontinuity occasioned by the sources of pollution and the self-cleaning process. To this effect, a survey was made to determine the physical-chemical, biological, climatological and hydrological variables in the longitudinal axis of the river and which utilized the QUAL2E model as a tool for simulating the concentrations of dissolved oxygen under different scenarios. It was possible to observe that many of the limnological variables studied in the Bonito rivulet suffer \"discontinuities\" due the entry of sewage. The concentrations of dissolved oxygen show a positive gradient from the source of the watercourse until station 4, and suffer a discontinuity after station 6, where the first discharge of sewage begins. The behaviour of this variable after the entry of sewage differed during the two periods studied. Furthermore, the \"Cluster\" and PCA (Principal Component Analyses) carried out upon the averages of the limnological variables distinguished different groups in the longitudinal profile of the Bonito rivulet. This distinction can be attributed to the above-mentioned entries of effluents and also resulting from the presence of the Curtume tributary. It can be verified that even with the natural assistance of the self-cleaning process, many of the variables studied fail to meet the standards of the receiving body, as stipulated by the CONAMA resolution number 20/86, in view of which, the present study suggests a degree of effluent treatment in order for these standards to be respected.

Este trabalho teve como objetivo estudar o comportamento espaço-temporal das variáveis limnológicas, no Ribeirão Bonito (SP) a fim de avaliar a descontinuidade ocasionada pelas fontes poluidoras e o processo de autodepuração. Para tanto, foram determinadas variáveis físico-químicas, biológicas, climatológicas e hidrológicas, no eixo longitudinal do rio e utilizado como ferramenta para diferentes cenários de simulações das concentrações de oxigênio dissolvido, o modelo QUAL2E. Foi possível observar, que muitas das variáveis limnológicas estudadas no Ribeirão Bonito sofrem \"descontinuidades\" devido à entrada de esgoto. As concentrações de oxigênio dissolvido têm um gradiente positivo da nascente até a estação 4, sofrendo uma descontinuidade após a estação 6 onde detecta-se o primeiro lançamento de esgoto. O comportamento dessa variável após a entrada de esgoto foi distinto nos dois períodos estudados. As análises de \"Cluster\" e PCA (Análise dos Componentes Principais), realizadas com as médias das variáveis limnológicas, distinguiram diferentes grupos no perfil longitudinal do ribeirão Bonito. Essa distinção pode ser atribuída às já citadas entradas de efluentes e também em decorrência da presença do tributário do Curtume. Pode-se constatar que mesmo com o auxílio natural do processo de autodepuração, muitas das variáveis estudadas não se enquadram aos padrões do corpo receptor conforme previsto pela resolução número 20/86 do CONAMA, sugerindo assim, neste trabalho, um grau de tratamento dos efluentes para que estes padrões sejam respeitados. / The objective of the present paper is to study the spatial-temporal behaviour of the limnological variables, in Bonito stream (SP), in order to evaluate the discontinuity occasioned by the sources of pollution and the self-cleaning process. To this effect, a survey was made to determine the physical-chemical, biological, climatological and hydrological variables in the longitudinal axis of the river and which utilized the QUAL2E model as a tool for simulating the concentrations of dissolved oxygen under different scenarios. It was possible to observe that many of the limnological variables studied in the Bonito rivulet suffer \"discontinuities\" due the entry of sewage. The concentrations of dissolved oxygen show a positive gradient from the source of the watercourse until station 4, and suffer a discontinuity after station 6, where the first discharge of sewage begins. The behaviour of this variable after the entry of sewage differed during the two periods studied. Furthermore, the \"Cluster\" and PCA (Principal Component Analyses) carried out upon the averages of the limnological variables distinguished different groups in the longitudinal profile of the Bonito rivulet. This distinction can be attributed to the above-mentioned entries of effluents and also resulting from the presence of the Curtume tributary. It can be verified that even with the natural assistance of the self-cleaning process, many of the variables studied fail to meet the standards of the receiving body, as stipulated by the CONAMA resolution number 20/86, in view of which, the present study suggests a degree of effluent treatment in order for these standards to be respected.

An 18-month study (July 2009 – December 2010) was conducted to determine the influence of four dams located in series along the Perak River, in Malaysia: Temengor, Bersia, Kenering and Chenderoh dams. The framework for investigation centered around the Serial Discontinuity Concept (SDC) and the Cascading Reservoir Continuum Concept (CRCC). In addition to reservoir, tailwater and riverine reach characteristics, the interacting influences of tributary streams and watersheds were addressed. Variables included in-situ environmental physical parameters, nutrients, seston concentration and transport, and fish assemblage characteristics. In-situ variables, water and seston samples, were recorded/collected monthly from all four reservoirs, their associated riverine sections, and their primary tributaries. Fish samples were collected by using experimental gill nets in reservoirs. Fish were enumerated taxonomically and total length and weight were measured for the bony-lipped barb, Osteochilus hasselti (Valenciennes, 1842). Hypotheses were tested using analyses of variance with permutations. Relationships were determined using correlation, and multivariate and regression analyses. The integrated influences of discontinuity and cascading on nutrient and seston transport dynamics and fish assemblages (except for relative condition and biomass of O. hasselti) were operative in dynamic juxtaposition along the river’s continuum, and depended on distance between dams and presence and size of tributary streams. However, principal tributaries along the four serial dams in the Perak River appeared to have little spatial influence on their respective system’s nutrient and seston dynamics due to dilution effects of mainstem discharges. Among all tributaries, only the Rui River depicted reversal of the serial discontinuity trend in its system. Even so, its influence on its system was limited. Effects of ecosystem fragmentation along the river’s continuum on in-situ, nutrients and seston transport dynamics, and fish assemblages existed, but not necessarily in line with the SDC nor in line with the CRCC. The dynamics of in-situ, nutrient, seston and fish assemblage parameters were more associated with land use, reservoir surface area and dam discharge. Results from this study generated a hypothesis that submerged woody vegetation in the reservoirs may augment and compensate lost nutrients, thereby minimizing functional impacts of serially-arranged dams.