Annual Summer Submersed Macrophyte Standing Stocks Estimated From Long-Term Monitoring Data in the Upper Mississippi River

Abstract System-scale restoration efforts within the Upper Mississippi River National Wildlife and Fish Refuge have included annual monitoring of submersed aquatic vegetation (SAV) since 1998 in four representative reaches spanning ? 440 river kilometers. We developed predictive models relating data (site-scale SAV abundance indices) to diver-harvested biomass, used back-estimate standing stock biomass between 2018, compared estimates with previous measures. modeled two morphologically distinct groups differing sampling efficiencies estimated each separately: first category only wild celery Vallisneria americana, which has long, unbranched leaves dominates lotic environments, while second 17 branched morphology species (e.g., hornwort Ceratophyllum demersum Canadian water weed Elodea canadensis) lentic environments. Wild accounted for approximately half total reaches, combined half, invasive (Eurasian watermilfoil Myriophyllum spicatum curly-leaf pondweed Potamogeton crispus), a fraction species, < 1.5%. Site-scale ranged from 0 535 g·m?2 (dry mass). observed increases most areas 2009 substantial 10 125 g·m?2) extensive impounded 2002 2007. Analyses also indicate transitional period 2007–2010 during changes trajectories were evident all start 9-y, 70% decrease southernmost area. Biomass provided new insights illustrated scales change that not previously apparent using traditional metrics. The ability estimate Long Term Resource Monitoring improves conservation through better understanding habitat food resources biota, improved goal setting projects quantification SAV-mediated structural effects such as anchoring sediments feedbacks quality.