Catchment urbanisation and increased benthic algal biomass in streams: linking mechanisms to management

Abstract

1. Urbanisation is an important cause of eutrophication in waters draining urban areas. We determined whether benthic algal biomass in small streams draining urban areas was explained primarily by small-scale factors (benthic light, substratum type and nutrient concentrations) within a stream, or by catchment-scale variables that incorporate the interacting multiple impacts of urbanisation (i.e. variables that describe urban density and the intensity of drainage or septic tank systems). 2. Benthic algal biomass was assessed as chlorophyll a density (chl a) in 16 streams spanning a rural-urban gradient, with both a wide range of urban density and of piped stormwater infrastructure intensity on the eastern fringe of metropolitan Melbourne, Australia. The gradient of urban density among streams was broadly correlated with catchment imperviousness, drainage connection (proportion of impervious areas connected to streams by stormwater pipes), altitude, longitude and median phosphorus concentration. Catchment area, septic tank density, median nitrogen concentration, benthic light (photosynthetically active radiation) and substratum type were not strongly correlated with the urban gradient. 3. Variation in benthic light and substratum type within streams explained a relatively small amount of variation in log chl a (3-11 and 1-13%, respectively) compared with between-site variation (39-54%). 4. Median chl a was positively correlated with catchment urbanisation, with a large proportion of variance explained jointly (as determined by hierarchical partitioning) by those variables correlated with urban density. Independent of this correlation, the contributions of drainage connection and altitude to the explained variance in chl a were significant. 5. The direct connection of impervious surfaces to streams by stormwater pipes is hypothesised as the main determinant of algal biomass in these streams through its effect on the supply of phosphorus, possibly in interaction with stormwater-related impacts on grazing fauna. Management of benthic algal biomass in streams of urbanised catchments is likely to be most effective through the application of stormwater management approaches that reduce drainage connection.

Pilot Study on the Effects of Partially Restored Riparian Plant Communities on Habitat Quality and Biodiversity along First-Order Tributaries of the Lower St. Johns River

“…Sabater et al [6] found that open nutrient-rich tributaries with warmer temperatures had significantly higher levels of algal biomass than shaded nutrient-poor streams. These results are consistent with other studies that have found interactions of various degrees between light levels, temperature and nutrient levels [5,9,15,16].…”

Response of algal metrics to nutrients and physical factors and identification of nutrient thresholds in agricultural streams

“…Light, climate, geology, land use, substrate size, and vegetation all have been identified as factors that can control algal populations in addition to nutrient conditions and related water chemistry parameters. In some cases, algal biomass and community structure are related more to factors measured at larger scales such as land use (Leland and Porter 2000;Snyder et al 2002;Taylor et al 2004) or patterns in hydrology (Biggs 1996;Biggs and Smith 2002) than to nutrients measured at local and ephemeral scales. Although broad-scale factors have been related to algal biomass and community structure, the hierarchical arrangement of these factors has received less attention (Stevenson 1997).…”

Effect of Wastewater Treatment Plant Effluent on Microbial Function and Community Structure in the Sediment of a Freshwater Stream with Variable Seasonal Flow

“…In this regard, Brooks et al (3) highlighted the considerable biomonitoring challenges to scientists and water resource managers of effluent-receiving streams with ephemeral or seasonally variable flows. Assessing the effects of effluent discharge on the health of receiving waterways is of considerable environmental consequence, especially in catchments with variable stream flows and where population pressure through urbanization and periurbanization is placing increasing pressure upon WWTP infrastructure and the health of freshwater ecosystems (15,39,43).…”