The Effects of Forested Riparian Zones on Stream Conditions

Forested riparian zones moderate stream temperatures, modify sediment transport, and improve stream health. Clearing of riparian areas due to agriculture or urban development can lead to major changes in stream ecosystem structure and function including higher water temperatures. A study was conducted to compare changes in temperature, dissolved oxygen (DO) concentration, pH, total dissolved solids (TDS) concentration, and turbidity in the streamflow along a 540-m stream with transitional changes in the characteristics of the riparian zones. The first 180-m of the reach have a 30-m to 65-m width forested riparian zone, followed by the remaining 360-m of a reach under incipient degradation in which grass grows and is mowed along both sides of the stream. Weekly monitoring has been performed in 8 stations along the study reach including grab water sampling, water quality, and flow velocity. Compared with the forested segment, the open reach has higher temperature (+2 ^oC), pH (+0.1), and total dissolved solids concentration (+0.03 g/l). The DO concentration remains almost constant along the forested reach, but drastically decrease along the clear segment (-2 mg/l). Forested riparian zones can reduce stream temperatures and maintain favorable concentrations of dissolved oxygen with a biological significance for the living organisms in the stream. Consequently, maintenance of forested riparian zones might provide benefits in mitigating some of the ecological effects of climate change on water temperature.