Examining the relative effects of nutrient loads and invasive Dreissena mussels on Lake Michigan’s food web using an ecosystem model

Lake Michigan;ecosystem modeling;food web;School for Environment and Sustainability

Boucher, NicholasMason, Doran ;

University of Michigan

关键词: Lake Michigan;    ecosystem modeling;    food web;    School for Environment and Sustainability;   

Others  :  https://deepblue.lib.umich.edu/bitstream/handle/2027.42/148814/Boucher_Nicholas_Thesis.pdf?sequence=1&isAllowed=y

瑞士|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

Lake Michigan has undergone ecosystem-wide changes over the past century dueto changing nutrient loads and an influx of invasive species. Zebra (Dreissenapolymorpha) and Quagga mussels (D. bugensis; collectively Dreissenid mussels) havebeen a particularly impactful invasive species, and currently account for the majority ofbenthic biomass in Lake Michigan. Dreissenid mussel filtration, along with decliningnutrient loads following the 1972 Great Lakes Water Quality Agreement, has reducedprimary productivity and caused oligotrophication in Lake Michigan’s offshore zone anda concurrent increase in nuisance algal blooms nearshore. However, the relative effects ofthese two factors on Lake Michigan’s food web remain a key knowledge gap.To quantify the relative effects of mussel grazing and nutrient loads on the LakeMichigan food web, I used the Lake Michigan Atlantis Model (LMAM) to predictbiomass changes of Lake Michigan species under six model scenarios. The Atlantismodel is a three-dimensional, spatially-explicit ecosystem model that takes into accountwater movement, seasonality, and food web interactions to dynamically predict biomassfor functional groups at each trophic level over time. I calibrated the model usingavailable agency food web data from 1994 to 2010, then ran 25 year simulations of 6different scenarios including three nutrient loads (double baseline load, half baselineload, and baseline 1994 load) and two mussel scenarios (mussels present or absent).Model results indicated that mussel grazing has a much greater relative impact on thefood web than changes in nutrient loads. Simulated mussel grazing on phytoplanktonradiated up the food web to cause resource limitation for prey fish and piscivores. Effectson functional group biomass owing to changes in phosphorus loading were largely masked by observed mussel effects. My findings contrast with other modeling studiesthat found nutrient loads also have a significant effect on productivity and biomass. Theseresults suggest that management strategies that increase nutrient flow into Lake Michiganwould have negligible positive effects on fish biomass.