engleski

Short-term effects of natural stream discharge on the water quality trends along two urban streams

Environmental changes associated with urbanization primarily modify stream morphology, which then further affects physical (discharge), chemical (water quality) and biological (biota) status of urban streams. We investigated the short-term effects of natural stream discharge on the water quality along two streams (Bliznec, B and Veliki potok, VP) flowing through Zagreb, Croatia. The research was conducted at six study sites stretched along the two urban streams during a two-week period in October 2017. Reference sites (B1, VP1) were located in the upper stream reaches within the Medvednica Nature Park. Other sites were aligned along an increasing urban gradient within Zagreb – sites B2 and VP2 were located in the middle, and B3 and VP3 in the lower stream reaches. The following physico-chemical parameters were measured every other day over the two-week period: stream discharge, water temperature and oxygen concentration, conductivity, chemical oxygen demand (CODKMnO4), and in-stream concentrations of nutrients (nitrites, nitrates, orhophosphates). Nutrients were the most variable parameters during the two-week period. Bliznec generally showed significantly higher discharge and oxygen levels compared to Veliki potok, which had significantly higher CODKMnO4 and nitrite concentrations. Middle and lower stream reaches had significantly higher temperature, nitrite and nitrate concentrations in comparison to the upper reaches. The data also revealed significant between-site and temporal changes of the physico-chemical parameters after a major storm event. Moreover, conductivity was found to correlate with discharge. Our findings indicate that urban streams are very dynamic ecosystems showing an increased sensitivity on environmental changes, such as anthropogenic influences and weather conditions.

urban streams ; stream discharge ; nutrient concentrations

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