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Ponds, wetlands, and shallow lakes (collectively "shallow waterbodies") are among the most biogeochemically active freshwater ecosystems. Measurements of gross primary production (GPP), respiration (R), and net ecosystem production (NEP) are rare in shallow waterbodies compared to larger and deeper lakes, which can bias our understanding of lentic ecosystem processes. In this study, we calculated GPP, R, and NEP in 26 small, shallow waterbodies across temperate North America and Europe. We observed high rates of GPP (mean 8.4 g O2 m−3 d−1) and R (mean −9.1 g O2 m−3 d−1), while NEP varied from net heterotrophic to autotrophic. Metabolism rates were affected by depth and aquatic vegetation cover, and the shallowest waterbodies had the highest GPP, R, and the most variable NEP. The shallow waterbodies from this study had considerably higher metabolism rates compared to deeper lakes, stressing the importance of these systems as highly productive biogeochemical hotspots. Plain Language Summary: Ecosystem metabolism is an important metric for understanding how an ecosystem uses and transforms energy and materials. In aquatic ecosystems, ecosystem metabolism is most often calculated by measuring oxygen. Oxygen is produced by aquatic plants and algae through photosynthesis, and oxygen is consumed by bacteria and other organisms through aerobic respiration. Oxygen production and consumption (metabolism) indicate how organic matter is flowing through the ecosystem, and whether an aquatic system is predominantly respiring (indicating it is a carbon source), or photosynthesizing (indicating it is a carbon sink). Metabolism rates in freshwater lakes scale with surface area and depth, but there are few metabolism rates calculated from oxygen measurements in shallow waterbodies. Ponds, wetlands, and shallow lakes are the most abundant freshwater systems on Earth and may function differently from larger lakes. In this study, we show that shallow systems are incredibly productive, with some of the highest rates of metabolism among aquatic ecosystems, and that depth is one of the most important factors affecting metabolism rates. Key Points: Shallow and small waterbodies have high but variable rates of gross primary production and respirationDepth plays a large role in metabolism ratesShallow waterbodies are some of the most productive freshwater ecosystems, with implications for carbon cycling and ecosystem dynamics [ABSTRACT FROM AUTHOR]

The ellipse, Venustaconcha ellipsiformis (Bivalvia: Unionidae), was first recorded in Minnesota from the Straight River in 1987, but we knew little of its distribution in the state, brooding behavior, glochidial host fish relationships or status. To examine these questions, we followed standard procedures to conduct an extensive, qualitative statewide mussel survey, described mantle flapping behavior from field and laboratory observations and identified suitable glochidia hosts in the laboratory and from naturally infested fishes. We found extant populations in five Mississippi River tributaries in southeastern Minnesota: the Cannon, Cedar, Root, Upper Iowa and Zumbro rivers. This appears to be the extent of its historic range in Minnesota as no valid records were found elsewhere. Among these, the largest population occurred in the headwaters of the Root River drainage, which was also the only drainage where we observed recent recruitment. Brooding V. ellipsiformis quickly flap a small mantle extension, often in response to passing shadows or jarring of the substrate, or their mantle extensions may be slowly undulated. We identified 11 fish species as suitable hosts for V. ellipsiformis glochidia in the laboratory: brook stickleback (Culaea inconstans), mottled sculpin (Cottus bairdii), slimy sculpin (C. cognatus), logperch (Percina caprodes), mud darter (Etheostoma asprigene), rainbow darter (E. caeruleum), Iowa darter (E. exile), fantail darter (E. flabbelare), Johnny darter (E. nigrum), banded darter (E. zonale) and blackside darter (P. maculata). Rainbow darter, fantail darter and blackside darter were also found naturally infested with V. ellipsiformis glochidia. Venustaconcha ellipsiformis should remain classified as a 'Threatened' species in Minnesota and management should include conserving populations within drainages due to its restricted range and likely low dispersal ability.

Abstract: Freshwater systems are increasingly threatened by human impacts. To effectively monitor and manage these systems, reference or baseline conditions need to be documented to establish restoration or management goals. Freshwater mussel (Unionoida) communities are in decline in many river systems worldwide. Yet there are few long‐term quantitative studies in relatively “pristine” habitats that could serve as “reference” locations. Here, we present the results of a 20‐year quantitative monitoring study of mussel assemblages in a federally protected river in the United States. We found significant declines in mussel abundance (41%) and species richness (16%) over the 20‐year period, while mussel species evenness and Shannon's diversity index values increased over time (19.3% and 12.1%, respectively). This, combined with an analysis of community composition change trajectories, suggests the declines were disproportionately higher for common species than for rare species. Variation in life‐history traits of macroinvertebrates is often used to assess the degree of degradation of aquatic systems. Using Haag's (2012) classification of mussel life‐history traits, we found the proportion of opportunistic species (fast growth, high reproductive output, short lifespan) decreased by 65.3%, while the proportion of equilibrium species (slow growth, long lifespan, lower investment in reproduction) increased by 54.6% and the proportion of periodic species (moderate‐to‐high growth rates, low‐to‐intermediate fecundity, lifespan and age at maturity) increased by 82.4%. There were modest changes in human population and land use in the catchment during our study period, and a change in the operation of a hydroelectric dam reduced discharge variability. Sediment size changed at several study sites, increasing at some sites while decreasing at others. This study occurred in one of the best‐protected and most pristine rivers in the upper Midwest of the United States, harbouring one of the region's most intact mussel fauna that could be used as a “reference” to set goals for the restoration of mussel fauna in other river systems. Despite the high quality and protection of this river system, we found slow declines in the mussel community but found no evidence that changes in land use, flow regime, water quality, the spread of invasive species or increased sedimentation were responsible for these declines. The slow decline of mussels and lack of specific causes in such a river underscore the imperilment of this fauna, and the need for more aggressive conservation, management and research approaches. [ABSTRACT FROM AUTHOR]

The winged mapleleaf mussel (Quadrula fragosa) is a federally-listed endangered species that once inhabited at least 34 river systems in 12 Midwestern states. Presently, the only known reproducing population exists [...]