Benthic nutrient sources to hypereutrophic Upper Klamath Lake, Oregon, USA

Abstract

Three collecting trips were coordinated in April, May, and August 2006 to sample the water column and benthos of hypereutrophic Upper Klamath Lake (OR, USA) through the annual cyanophyte bloom of Aphanizomenon flos-aquae. A pore-water profiler was designed and fabricated to obtain the first high-resolution (centimeter-scale) estimates of the vertical concentration gradients of macro- and micronutrients for diffusive-flux determinations. A consistently positive benthic flux for soluble reactive phosphorus (SRP) was observed with solute release from the sediment, ranging between 0.4 and 6.1 mg/m(2)/d. The mass flux over an approximate 200-km(2) lake area was comparable in magnitude to riverine inputs. An additional concern related to fish toxicity was identified when dissolved ammonium also displayed consistently positive benthic fluxes of 4 to 134 mg/m(2)/d, again comparable to riverine inputs. Although phosphorus was a logical initial choice by water quality managers for the limiting nutrient when nitrogen-fixing cyanophytes dominate, initial trace-element results from the lake and major inflowing tributaries suggested that the role of iron limitation on primary productivity should be investigated. Dissolved iron became depleted in the lake water column during the course of the algal bloom, while dissolved ammonium and SRP increased. Elevated macroinvertebrate densities, at least of the order of 10(4) individuals/m(2), suggested that the diffusive-flux estimates may be significantly enhanced by bioturbation. In addition, heat-flux modeling indicated that groundwater advection of nutrients could also significantly contribute to internal nutrient loading. Accurate environmental assessments of lentic systems and reasonable expectations for point-source management require quantitative consideration of internal solute sources.

Changes in benthic nutrient sources within a wetland after hydrologic reconnection

“…The present study extends and builds on previous nutrient-transport studies focused on the adjacent lake [16] by posing the following five hypotheses. We used this opportunity to investigate the multiyear temporal changes in the chemistry and biology that occur to the benthos and water column after this approach to wetland restoration was implemented.…”

“…These changes have transformed the lake to a hypereutrophic status with massive, summer cyanobacterial blooms dominated by the nitrogen-fixing Aphanizomenon flos-aquae [23]. Because the growth of these blooms is supported by the flux of nutrients-phosphorus in particular but potentially other macro-and micronutrients as well-from the lakebed [16], the contribution of the benthos in the newly flooded wetlands to the overall nutrient balance is of considerable interest. As the bloom declines and cells senesce in late July to early August, oxygen may be depleted in the water column and lakebed.…”

“…Nonmetallic porewater profilers, designed for nutrient and trace-metal sampling (U.S. Patent 8,051,727 B1 [16]) were deployed in triplicate at each sampling site. Profilers collected samples from six independent depths through a series of filters: the shallowest approximately 1 cm above the sediment-water interface and the other five approximately 1, 2, 3.3, 5.5, and 10 cm below that interface, respectively, to characterize dissolved-solute vertical gradients.…”

“…Just prior to profiler retrieval, water-column profiles of pH, specific conductivity, temperature, dissolved oxygen, and oxidation-reduction potential were Benthic nutrient sources after engineered levee breaches Environ. Samples were then frozen at À818C in darkness for preservation until spectrophotometrically analyzed within three months by methods described in Thompson et al [33] (see also [16] and Franson [34]). Chem.…”

Microcystins, nutrient dynamics, and other environmental factors during blooms of non-microcystin-producingAphanizomenon flos-aquaein Upper Klamath Lake, Oregon, 2009

“…In addition, previous work showed depletion in dissolved iron concentrations by the end of the late-season (Aug) bloom period, relative to early season conditions (Apr-May; Kuwabara et al 2009). Iron is known to promote microcystin production in other systems (Sevilla et al 2008, Alexova et al 2011, so the seasonal depletion observed in 2006 may signify a possible role for iron availability in microcystin occurrence in Upper Klamath Lake.…”