Ecosystem metabolism in shallow coastal lagoons: patterns and partitioning of planktonic, benthic, and integrated community rates

Abstract

Net ecosystem metabolism (NEM) provides a quantifiable and integrative method for assessing the ecological responses of aquatic ecosystems to anthropogenic disturbance and has been shown to positively relate to nutrient enrichment in some systems. We measured NEM to determine the trophic status of 4 coastal lagoons receiving a range of nutrient loads on the Virginia/ Maryland portion of the Delmarva Peninsula, USA. From July 2007 to July 2008, we used the component technique to assess NEM by developing photosynthesis−irradiance curves for both the water column and sediments approximately monthly; we added macroalgal incubations in the summer of 2008. We also measured in situ NEM by the open water method using 2 to 3 wk deployments of data sondes. Component incubations indicated net autotrophy in all 4 lagoons for March to October. No significant relationship existed between NEM and total nitrogen load overall, except for reduced autotrophy in the most enriched system. Light availability, sediment organic content, temperature and depth were all important regulators of NEM. Inclusion of macroalgal metabolism during summer 2008 had varied effects on system NEM. Open water and component methods gave divergent results. We attribute these differences to the adjacent marshes and the assumptions inherent in the 2 methods, demonstrating the need for careful attention to the method of choice for estimating system metabolism in these highly variable, shallow photic systems. Overall, NEM was net autotrophic, dominated by phytoplankton production across our study lagoons, and controlled by multiple factors.KEY WORDS: Net ecosystem metabolism · Primary production · Respiration · Coastal lagoon · Phytoplankton · Microphytobenthos · Macroalgae Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 458: 21-38, 2012 22 shellfish species (Beck et al. 2001, Able 2005, EPA 2008). The close proximity of shallow marine systems to land, their small volumes and relatively long residence times, and the penetration of light to the benthos make these systems particularly susceptible to nutrient enrichment (Duarte 1995, Bricker et al. 1999). Microphytobenthos (MPB), however, may help mediate the response of shallow systems to nutrient loading (Tobias et al. 2003, Anderson et al. 2010.Although nitrogen loads to coastal lagoons are of a magnitude similar to those of deeper estuaries, responses in shallow lagoons appear to be quite different, likely because of enhanced benthic− pelagic coupling (Nixon et al. 2001). An illuminated benthos results in a significant contribution of MPB, seagrasses and macroalgae to total system production. Under extremely high nitrogen loads, however, bloom-forming macroalgae and, ultimately, phytoplankton can dominate, shading out MPB, seagrasses and slow-growing macroalgae (Borum & Sand-Jensen, 1996, Valiela et al. 1997.Interactions between autotrophic communities are complex and predictive patterns between nutrient loading and a single component of the sys...

Ecosystem metabolism along a colonization gradient of eelgrass (Zostera marina) measured by eddy correlation

“…1). This differs from results of previous core incubation studies in the VCR lagoons that have shown unvegetated sediments were net autotrophic during at least part of the year (McGlathery et al 2001;Tyler et al 2003;Giordano et al 2012), but agrees well with the results found by Hume et al (2011) using the eddy correlation technique (see Fig. 2).…”

Spatiotemporal variability of light attenuation and net ecosystem metabolism in a back-barrier estuary

“…In fact, modest net autotrophy (on a monthly basis) prevailed during the summer season at vegetated sites but not at unvegetated sites. The rates of P g and R t we estimated, which were typically between 200 and 400 mmol O 2 m −2 d −1 , are comparable to those measured in other temperate ecosystems dominated by Zostera marina (Howarth et al, 2014), and net autotrophy in these low-nutrient environments is consistent with other coastal lagoons in the region (Giordano et al, 2012;Stutes et al, 2007). While the overall metabolic balance (P g /R t ) of Chincoteague Bay is difficult to assess, given large differences in metabolic balance across a range of depths and nutrient enrichment levels, we made a simple calculation whereby the mean rates of net ecosystem metabolism at CB10 were multiplied by the area of SAV in 2015 (30 km 2 ) and rates from CB06 are multiplied by the remaining area without SAV (276 km 2 ).…”

Pelagic contribution to gross primary production dynamics in shallow areas of York River, VA, U.S.A.

“…This study aims to (1) examine the spatial and long‐term temporal variations of pelagic GPP, ecosystem GPP, and pelagic contribution to ecosystem production across multiple shallow‐water ecosystems in the York River, and (2) investigate the succession in ecosystem assemblages of primary producers as the response to the change of nutrient loading conceptually. The ecosystem GPP is estimated using the open water diel oxygen method (Odum ; Swaney et al ; Cole et al ; Howarth and Michaels ; Caffrey ; Staehr et al ; Giordano et al ). The open water diel oxygen method, rather than measuring ecosystem GPP directly, extrapolates the production from the in situ observed dissolved oxygen (DO) concentration data based on the mass balance of DO dynamics.…”