Assessment of the impact of land cover and beneficial management practices on water quality in complex watersheds – challenges and research opportunities ahead

English Abstract:

Many watersheds are characterized by heterogeneous or mixed land cover. As such, urban, agricultural, industrial and forested areas are often found in the same watershed. In the urban portion, water quality tends to be governed by variability in both dry and wet conditions; while in the agricultural and forested portions, it is mostly governed by wet conditions producing significant runoff. When mobilized sources of contaminants are transported, impaired water quality conditions can arise in surface and ground waters. The transport can be altered by managing sources and/or modifying both hydrological and sedimentlogical connectivity. From a surface hydrology point of view, the watershed represents the basic unit to assess the impact of various land covers and Beneficial Management Practices (BMPs) on water quality and ultimately on sustainable development. One way to accomplish this task is to apply an integrated modelling framework at the watershed scale. Several applications of such a modelling framework have demonstrated that evaluation of the effects of land covers and BMPs cannot be solely based on analysis of overland loads but must also focus on in-stream concentrations and loads as non-linear behaviors characterize the outcomes. A comprehensive cumulative impact assessment must further be performed and based on cost and environmental benefit analysis, as well as on biological integrity indices and probability of exceeding ecotoxicological criteria. Although models are continuously improved, recent field surveys highlight the need for further investigate sediment dynamics in the stream network as well as in the riparian zone. This is one example of the real challenges ahead. This presentation will discuss the challenges and research opportunities of modelling key processes at meaningful spatial and temporal scales with an emphasis on the modelling of vegetated filters and wetlands.