Nutrient load concept-reservoir vs. bay impacts: a case study from a semi-arid watershed.

Large flow-through reservoirs and lakes possess environmental gradients and monitoring programs are mostly adapted for cost and time effectiveness. Bay areas are often more isolated from the main water body and are likely to have unobserved different environmental processes and impacts. This study was performed at the Itaparica Reservoir, São Francisco River, located in semi-arid Northeast Brazil, with dendritic form. Water residence time in the Icó-Mandantes Bay was estimated by hydrodynamic flow and transport simulations. The P-chlorophyll a relationship was used to develop the P use efficiency coefficient for critical P load estimation of 25 µg P L-1. Phosphorus sources and input rates into a bay and the respective reservoir were calculated and compared regarding their different origins for the period after flooding (1988) and for 2013. After impoundment, the P load highly exceeded the carrying capacity because of leaching and mineralization processes. In 2013, P inputs were still above this threshold, whereas inflow and sub-basin P export during the rainy season were crucial. But eutrophication processes have increased in the bay relative to the main water body. Hence, water in hydraulic isolated parts is prone to eutrophication processes, thus, bays have to be specially considered in water resource management.

Simulations of nutrient emissions from a net cage aquaculture system in a Brazilian bay.

Hydrodynamics and transport simulations were conducted with the modeling software TELEMAC-2D on Icó-Mandantes bay, a branch of the Itaparica reservoir. The bay has a maximal operational water level amplitude of 5 m and is suffering from eutrophication and algae bloom. Therefore, we investigated low and high water level scenarios with two different high resolution meshes, with the purpose to deeper understand their impact on transport of substances and to improve the watershed management. In particular, nutrient emissions from a hypothetical net cage aquaculture system located in the bay were investigated on half-year cycles. We observed a relevant impact on water quality for a tilapia production of 130 t y(-1); i.e. after 6 months' simulation we obtained around 8 µgP L(-1) and 6 µgP L(-1) at the source of emissions, for low and high water scenarios, respectively.

Effects of 66 years of water management and hydroclimatic change on the urban hydrology and water quality of the Panke catchment, Berlin, Germany.

Long-term records of combined stream flow and water chemistry can be an invaluable source of information on changes in the quantity and quality of water resources. To understand the effect of hydroclimate and water management on the heavily urbanized Panke catchment in Berlin, Germany, an extensive search, collation and digitization of historic data from various sources was undertaken. This integrated a unique 66-year spatially distributed record of stream water quality, a 21-year record of groundwater quality and a 31-year stream flow record. These data were analysed in the context of hydroclimatic variability, as well as the history and technological evolution of water resource management in the catchment. To contextualize the effect of droughts, "average" and wet years the Standard Precipitation Index (SPI) was applied. As upstream sites have been less regulated by human impacts, the flow regime is most sensitive to changes in hydroclimatic conditions, while downstream sites are more influenced by wastewater effluents, urban storm drains and inter-basin transfers for flood alleviation. However, at all sites, a general increase in maximum event discharge was observed until a recent drought, starting in 2018. In general, water quality in the catchment has gradually improved as a result of management change and increasingly effective wastewater treatment, though in some places legacy and/or contemporary urban and rural groundwater contamination may be affecting the stream. Hydroclimatic changes, particularly drought years can affect water quality classes, and alter the chemostatic/dynamic behaviour of catchment export patterns. These insights from the Panke catchment underline the importance of strategic adaptation and improvement of water treatment and water resource management in order to enhance the quality of urban water courses. It also demonstrates the importance of long-term integrated data sets.