Abstract
Many estuaries are becoming increasingly eutrophic from human activities within their catchments. Nutrient loads often are used to assess risk of eutrophication to estuaries, but such data are expensive and time consuming to obtain. We compared the percent of fertilized land within a catchment, dissolved inorganic nitrogen loads, catchment to estuary area ratio and flushing time as predictors of the proportion of macroalgae to total vegetation within 14 estuaries in south-eastern Australia. The percent of fertilized land within the catchment was the best predictor of the proportion of macroalgae within the estuaries studied. There was a transition to a dominance of macroalgae once the proportion of fertilized land in the catchment exceeded 24%, highlighting the sensitivity of estuaries to catchment land use.
Highlights
Estuaries are well recognized for their ecological and economic value, by supporting diverse natural communities, highly productive fisheries, and recreational amenity (McLusky & Elliott, 2004)
The results show that land use is a strong predictor of the proportion of macroalgae to total vegetation within south-eastern Australian estuaries
The proportion of the catchment receiving fertilization was a better predictor of the macroalgae to total vegetation (MA):TV ratio than was areal dissolved inorganic nitrogen (DIN) load, which we have previously suggested to be a better predictor of MA:TV in these estuaries than total nitrogen (TN) or total phosphorous (TP) loads (Woodland et al, 2015)
Summary
Estuaries are well recognized for their ecological and economic value, by supporting diverse natural communities, highly productive fisheries, and recreational amenity (McLusky & Elliott, 2004). Being at the terminus of drainage basins, estuaries are impacted by increased nutrient loads delivered to the coastal zone. Intensive monitoring of both catchments and estuaries has clearly and consistently implicated nutrient loads, in particular nitrogen, as the drivers of multiple adverse ecological responses, including initiation of algal blooms, hypoxia and alteration of secondary production (Hauxwell & Valiela, 2004; Conley et al, 2009). Detailed time-series of nutrient-loading data are not readily available for most estuaries around the world, and a widely applicable and pragmatic approach is required to assess ecological risk and guide land use planning and management targets more generally. The effectiveness of land use data at acting as a proxy for risk to estuaries will depend on
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