Predicting coastal eutrophication from land-use:an empirical approach to small non-stratified estuaries

Abstract

Few models exist to directly and quantitatively predict the effect of land-use on coastal water quality even though it is recognized that land-use is a major determinant of coastal water quality. Such models are needed because (1) land-use is a major source of nutrients transported to estuaries, (2) land-use integrates multiple factors that may determine the mean algal biomass and (3) land-use is more easily managed than single nutrients when nutrient sources are nonpoint Regression models accurately predict lake eutrophication as a funct~on of land-use. Similar models do not exist for estuaries. A data set was compiled for 15 estuanes in Pnnce Edward Island (PEI), Canada, that includes phytoplankton biomass as chlorophyll a (chl), total phosphorus (TP), total nitrogen (TN), estuary morphometry and land-use characteristics. A regression model predicting chl as a function of estuary volume and area of agriculture was developed. This model accounts for 68% of the variance in chl, a level similar to that of models based on TN (r2 = 0.72) or total phosphorus (r2 = 0.66). The estuary models based on land-use and total nutrients demonstrate low yields of chl when compared to analogous lake models; this low yield is likely attributable to high levels of herbivory by suspension feeding mussels. Despite these low yields, the pattern between chl and land-use is sufficiently accurate such that environmental managers can predict the effects of changing land-use on estuary water quality in PE1 with a known level of error.

Bay-scale spatial growth variation of mussels Mytilus edulis in suspended culture, Prince Edward Island, Canada

“…Samples taken over shorter time scales suggest the importance of both resuspension and estuarine flushing to seston concentrations (Grant et al in press). The influence of mussels has also been suggested in calculations by Meeuwig (1999) that indicated a strong negative relationship between mussel and phytoplankton biomass in PEI embayments with mussel culture.…”

“…Rainfall in May and June 1998 was 3 to 6 times more than in 1999 (Environment Canada climate summaries), potentially resulting in nutrient enrichment from agricultural runoff and subsequent phytoplankton blooms in Winter Bay. Agricultural activities on PEI exert a large influence on nutrient levels within surrounding embayments (Meeuwig 1999). In 1999, meat growth had a slow start, but poor food supplies early in the year are not obvious from the seston record.…”

“…Samples taken over shorter time scales suggest the importance of both resuspension and estuarine flushing to seston concentrations (Grant et al in press). The influence of mussels has also been suggested in calculations by Meeuwig (1999) that indicated a strong negative relationship between mussel and phytoplankton biomass in PEI embayments with mussel culture.There appeared to be a fundamental temporal change in seston quality and quantity between years beyond spatial differences in seston flux. The negative relationship between SPM and % POM in 1998 suggests that resuspended particles were important in some of the seston samples (Hawkins et al 1996(Hawkins et al , 1998.…”

Our evolving conceptual model of the coastal eutrophication problem

“…First, although it is possible to develop Vollenweider-type models for some sets of coastal lagoons (Boynton et al 1996) and estuaries, these models are significantly different from the lake models. For example, Meeuwig (1999) developed empirical models that describe variability of phytoplankton biomass among 15 Canadian estuaries as functions of land use in the watersheds. These models show that the chlorophyll yield, per unit N delivery, is 10 times smaller than the mean chlorophyll yield derived from comparable lake models.…”

Assessment of spatial environmental quality status in Ria de Aveiro (Portugal)

“…Due to the shallow depth and relatively weak exchange with the open sea, these systems are particularly vulnerable to eutrophication (with the concomitant decline in environmental quality), which is recognised as a major problem worldwide (e.g. Meeuwing, 1999;Flindt et al, 1999;Cloern, 2001;Lillebø et al, 2005).…”