Enhanced bioavailability of dissolved organic matter (DOM) in human-disturbed streams in Alpine fluvial networks

The influence of human activities on the role of inland waters in the global carbon (C) cycle is poorly constrained. In this study, we investigated the impact of human land use on the sources and biodegradation of dissolved organic matter (DOM) and its potential impact on bacterial respiration in 10 independent catchments of the Lake Geneva basin. Sites were selected along a gradient of human disturbance (agriculture and urbanization) and were visited twice during the winter high-flow period. Bacterial respiration and DOM bioavailability were measured in the laboratory through standardized dark bioassays, and the influence of human land uses on DOM sources, composition and reactivity was assessed from fluorescence spectroscopy. Bacterial respiration was higher in agro-urban streams but was related to a short-term bioreactive pool (0–6 d of incubation) of autochthonous origin, whose relative contribution to the total DOM pool increased with the degree of human disturbance. On the other hand, the degradation of a long-term (6–28 d) bioreactive pool related to terrestrial DOM was independent from the catchment land use and did not contribute substantially to aquatic bacterial respiration. From a greenhouse gas emission perspective, our results suggest that human activities may have a limited impact on the net C exchanges between inland waters and the atmosphere, as most CO2 fixed by aquatic producers in agro-urban streams is cycled back to the atmosphere after biomineralization. Although seasonal and longitudinal changes in DOM sources must be considered, the implications of our results likely apply more widely as a greater proportion of autochthonous-DOM signature is a common feature in human-impacted catchments. Yet, on a global scale, the influence of human activities remains to be determined given the large diversity of effects of agriculture and urbanization on freshwater DOM depending on the local environmental context.

Runoff Prediction Based on the Discharge of Pump Stations in an Urban Stream Using a Modified Multi-Layer Perceptron Combined with Meta-Heuristic Optimization

Runoff in urban streams is the most important factor influencing urban inundation. It also affects inundation in other areas as various urban streams and rivers are connected. Current runoff predictions obtained using a multi-layer perceptron (MLP) exhibit limited accuracy. In this study, the runoff of urban streams was predicted by applying an MLP using a harmony search (MLPHS) to overcome the shortcomings of MLPs using existing optimizers and compared with the observed runoff and the runoff predicted by an MLP using a real-coded genetic algorithm (RCGA). Furthermore, the results of the MLPHS were compared with the results of the MLP with existing optimizers such as the stochastic gradient descent, adaptive gradient, and root mean squared propagation. The runoff of urban steams was predicted based on the discharge of each pump station and rainfall information. The results obtained with the MLPHS exhibited the smallest error of 39.804 m3/s when compared to the peak value of the observed runoff. The MLPHS gave more accurate runoff prediction results than the MLP using the RCGA and that using existing optimizers. The accurate prediction of the runoff in an urban stream using an MLPHS based on the discharge of each pump station is possible.

Environmental Determinates of Distribution for Dragonfly Nymphs (Odonata: Anisoptera) in Urban and Non-Urban East Texas Streams, USA

We collected environmental and habitat data for nymphs of 12 dragonfly species (Odonata: Anisoptera) from 91 stream sites throughout eastern Texas, including urban and non-urban locations. Understanding the relationship of dragonflies to habitat structure and other environmental variables is crucial for the purpose of conserving these insects and better using them as predictive tools for water quality assessments, and refining tolerance values. The objectives of this study were to determine the key environmental variables influencing the diversity and distribution of dragonflies in eastern Texas streams, and further determine if differences in those factors could be observed between urban and nonurban sites. We collected samples separately from benthic habitats and woody snag habitats. Significantly fewer sites were observed to have dragonfly species on snag habitat (mean = 1.25) compared to benthic samples (mean = 14.67) (t-test, p = 0.001). The number of dragonfly species collected among non-urban streams (mean = 9.83) was not significantly different than urban streams (mean = 6.08; t-test, p = 0.07). Detrended correspondence analysis of benthic and snag habitat data collected from non-urban and urban locations showed that most of the species are oriented most closely to benthic habitats in non-urban streams. Snag habitat was shown to be poorly ordinated for all of the species. A canonical correspondence analysis of 29 water quality and habitat variables as environmental determinants of dragonfly diversity and distribution showed that distributional relationships among species are complex and often described by multiple environmental factors.

Dispersed urban-stormwater control improved stream water quality in a catchment-scale experiment

Traditional approaches to urban drainage degrade receiving waters. Alternative approaches have potential to protect downstream waters and provide other benefits to cities, including greater water security. Their widespread adoption requires robust demonstration of their feasibility and effectiveness. We conducted a catchment-scale, before-after-control-reference-impact experiment to assess the effect of dispersed stormwater control on stream ecosystems. We used a variant of effective imperviousness (EI), integrating catchment-scale stormwater runoff impact and stormwater-control-measure (SCM) performance, as the measure of experimental effect. We assessed the response of water quality variables in 6 sites on 2 streams, following SCM implementation in their catchments. We compared changes in those streams over 7 years, as SCM implementation increased, to the 12 preceding years, and over the 19 years in 3 reference and 2 control streams. SCMs reduced phosphorus and nitrogen concentrations and temperature, and increased electrical conductivity; with effect size negatively correlated with antecedent rain. SCM-induced reductions in phosphorus and temperature were of a similar magnitude to increases from urban development, when assessed as a function of change in EI. Nitrogen reductions were observed, even though concentrations among sites were not correlated with EI, being more influenced by septic tank seepage. SCMs had no effect on suspended solids concentrations, which were lower in urban streams than in reference streams. This experiment strengthens the inference that urban stormwater drainage increases contaminant concentrations in urban streams, and demonstrates that such impacts are reversible and likely preventable. SCMs reduce contaminant concentrations by reducing the frequency and magnitude of uncontrolled drainage flows and augmenting reduced baseflows. Increased EC and reduced temperature are likely a result of increased contribution of groundwater to baseflows. The stormwater control achieved by the experiment did not fully return phosphorus or nitrogen concentrations to reference levels, but their responses indicate such an outcome is possible in dominant conditions (up to ~20 mm of 24-h antecedent rain). This would require nearly all impervious surfaces draining to SCMs with large retention capacity, thus requiring more downslope space and water demand. EI predicts stream water quality responses to SCMs, allowing better catchment prioritization and SCM design standards for stream protection.

Stream or Discharge: Using the Hydrosocial Cycle to Explore the Meanings of the Waimapihi Stream in Te Whanganui-a-Tara-Wellington, Aotearoa-New Zealand

<p>Aotearoa-New Zealand’s urban streams are complex and diverse but have been degraded and neglected for years. For the most part, hegemonic management regimes are technocratic, separating streams into discrete parts, and thus have failed to improve or maintain the state of urban streams. The hydrosocial cycle is a way of exploring streams that takes account of whole systems, flows of water, more than humans, infrastructure and technology, and the social structures and institutions that make up water. The framework has been used to study the impacts of urbanisation on water around the world, including issues around stormwater, wastewater, water supply, and rivers, but it has rarely been used to study buried urban streams. This research uses a case study of the Waimapihi Stream in Te Whanganui-a-Tara-Wellington, Aotearoa-New Zealand to explore how the hydrosocial cycle could be used to understand urban streams. A hydrosocial approach, alongside a more-than-human methodology, demonstrated the varying meanings of the stream, including those of the different phases along its length. Connections to the buried section of the Waimapihi arose through the presence of fish, physical markers, and stories, but there was dissatisfaction with the extent of these. As a result, alternative methods of connection such as windows to the stream and areas of it to be daylighted were explored. A hydrosocial approach enabled an examination of meanings and values of the Waimapihi Stream; to encourage critical analysis of how streams are defined and how they are managed. This demonstrated that the hydrosocial cycle provides a valuable framework for understanding urban streams, as it encompasses the various components that make up urban streams and is flexible enough to explore the diversity between and within them. Key words: Hydrosocial cycle, more-than-human, stormwater, wastewater, urban streams, Te Whanganui-a-Tara-Wellington, Aotearoa-New Zealand.</p>

Stream or Discharge: Using the Hydrosocial Cycle to Explore the Meanings of the Waimapihi Stream in Te Whanganui-a-Tara-Wellington, Aotearoa-New Zealand

<p>Aotearoa-New Zealand’s urban streams are complex and diverse but have been degraded and neglected for years. For the most part, hegemonic management regimes are technocratic, separating streams into discrete parts, and thus have failed to improve or maintain the state of urban streams. The hydrosocial cycle is a way of exploring streams that takes account of whole systems, flows of water, more than humans, infrastructure and technology, and the social structures and institutions that make up water. The framework has been used to study the impacts of urbanisation on water around the world, including issues around stormwater, wastewater, water supply, and rivers, but it has rarely been used to study buried urban streams. This research uses a case study of the Waimapihi Stream in Te Whanganui-a-Tara-Wellington, Aotearoa-New Zealand to explore how the hydrosocial cycle could be used to understand urban streams. A hydrosocial approach, alongside a more-than-human methodology, demonstrated the varying meanings of the stream, including those of the different phases along its length. Connections to the buried section of the Waimapihi arose through the presence of fish, physical markers, and stories, but there was dissatisfaction with the extent of these. As a result, alternative methods of connection such as windows to the stream and areas of it to be daylighted were explored. A hydrosocial approach enabled an examination of meanings and values of the Waimapihi Stream; to encourage critical analysis of how streams are defined and how they are managed. This demonstrated that the hydrosocial cycle provides a valuable framework for understanding urban streams, as it encompasses the various components that make up urban streams and is flexible enough to explore the diversity between and within them. Key words: Hydrosocial cycle, more-than-human, stormwater, wastewater, urban streams, Te Whanganui-a-Tara-Wellington, Aotearoa-New Zealand.</p>