Changes in benthic nutrient sources within a wetland after hydrologic reconnection

Abstract

Removing dams and levees to restore hydrologic connectivity and enhance ecosystem services such as nutrient removal has been an increasingly common management practice. In the present study, the authors assessed geochemical and biological changes following engineered levee breaches that reconnected eutrophic Upper Klamath Lake and Agency Lake, Oregon, USA, to an adjacent, historic wetland that had been under agricultural use for the last seven decades. Over the three-year study, the reconnected wetland served as a benthic source for both macronutrients (dissolved organic carbon [DOC], soluble reactive phosphorus [SRP], and ammonia) and micronutrients (dissolved iron and manganese). The magnitude of those benthic sources was similar to or greater than that of allochthonous sources. The highest DOC benthic flux to the water column occurred immediately after rewetting occurred. It then decreased during the present study to levels more similar to the adjacent lake. Dissolved ammonia fluxes, initially negative after the levee breaches, became consistently positive through the remainder of the study. Nitrate fluxes, also initially negative, became negligible two years after the levee breaches. In contrast to previous laboratory studies, SRP fluxes remained positive, as did fluxes of dissolved iron and manganese. Our results indicate that the timescales of chemical changes following hydrologic reconnection of wetlands are solute-specific and in some cases extend for multiple years beyond the reconnection event. During the present study, colonization of the reconnected wetlands by aquatic benthic invertebrates gradually generated assemblages similar to those in a nearby wetland refuge and provided further evidence of the multiyear transition of this area to permanent aquatic habitat. Such timescales should be considered when developing water-quality management strategies to achieve wetland-restoration goals.

Benthic processes affecting contaminant transport in Upper Klamath Lake, Oregon

“…In contrast to SRP and ammonia, no positive benthic fluxes were observed for nitrate. This is consistent with previously published nitrate fluxes for Upper Klamath Lake (Kuwabara and others, 2009;Kuwabara, 2012a). Nitrate flux was −0.55 ± 2.34 mg-N m −2 d −1 (range = −12.42 to 0.00 mg-N m −2 d −1 , n=65; table 3).…”

“…Data described in this section represent dissolved trace-element concentrations from surface-grab samples collected approximately 0.5 m below the surface using a clean technique ("Methods" section; table 7). As previously reported for Upper Klamath Lake, many of those dissolved metals (for example, cadmium, cobalt, lead, nickel, and zinc) were present at dissolved concentrations below or near detection limits (Kuwabara and others, 2009;Kuwabara, 2012a). The discussion below focuses on water-column traceelement data for dissolved iron (Fe), manganese (Mn), and arsenic (As).…”

The upside-down river: Reservoirs, algal blooms, and tributaries affect temporal and spatial patterns in nitrogen and phosphorus in the Klamath River, USA

“…However, it is possible for a reservoir to temporally shift from being a sink to a source (Jones, 2010;Kraus et al, 2011;Cole et al, 2007) and seasonal changes in the composition of outflows influence downstream processing (Kling et al, 2000;Goodman et al, 2010). While UKL has previously been described as a source of nutrients (Kuwabara et al, 2012), additional reservoirs within the Klamath River appear to have varying effects on downstream trends in N versus P. Identifying stoichiometric relationships between N and P is critical for understanding ecological processes, therefore N and P should be addressed both individually and together, and in the context of other water quality characteristics.…”

“…(Snyder and Morace, 1997;Abrams and Jarrell, 1995). A high proportion of the P in surface sediments of UKL is considered bioavailable (Simon and Ingle, 2011), and consistent positive benthic fluxes of SRP from UKL sediments have been observed from April through August (Kuwabara et al, 2007(Kuwabara et al, , 2012. High P-availability is considered the controlling factor in the development of large cyanobacteria blooms in UKL (NRC, 2004).…”

Water and nutrient budgets for Vancouver Lake, Vancouver, Washington, October 2010-October 2012

“…The Fick's law model does not incorporate the contributions to the flux from wind resuspension or benthic fauna, and therefore are considered underestimates of the true benthic flux (Kuwabara and others, 2012).…”