A Multi-element Sediment Record of Hydrological and Environmental Changes From Lake Erie since 1800OHSU-RS-1575 ABSTRACT:
Concentrations of aluminum, arsenic, barium, beryllium, cadmium, calcium, chromium, cobalt, copper, iron, lead, magnesium, manganese, molybdenum, nickel, potassium, selenium, sodium, tin, titanium, vanadium, and zinc were measured in a surface sediment core from the Sandusky basin of Lake Erie to detail the history of hydrological and environmental changes back to 1800. The results from hierarchical cluster and principal component analyses revealed four elemental groups. All the trace elements clustering with aluminum, iron, and manganese in Group I were enriched due to increased inputs from anthropogenic sources. The two conservative elements sodium and potassium clustering in Group II showed patterns of changes like those of water-level fluctuations. The two carbonate elements calcium and magnesium clustering in Group III showed intriguing but complex carbonate biogeochemistry associated with biogenic production, organic acid-induced dissolution and dilution by organic and aluminosilicate materials. The terrigenous element titanium in Group IV experienced two stages of depletion from increased organic fluxes in the 1820s and 1950s. Following the enactments of stringent regulations in the early 1970s, many of these elemental inputs have reduced considerably. But the concurrent reductions in the Sandusky basin were much slower than previously thought. Large increases in inputs from local storages (internal loading) were required to account for the slow reductions. The increased internal loading was caused by augmented organic materials from accelerated eutrophication which facilitated the transfer, transport, and cycling of many trace metals. This work has implications in ongoing research efforts to tackle the eutrophication problem because the complex ecosystem including the internal loading has changed considerably over the past two centuries.
DOI: 10.1007/s10933-017-9953-3 VOLUME: 58 ISSUE: 1 LENGTH: 19 pages
A Decline in Benthic Algal Production May Explain Recent Hypoxic Events in Lake Erie's Central BasinOHSU-RS-1574 ABSTRACT:
Since the late 1990s, the central basin of Lake Erie has reputedly experienced an increase in the frequency and severity of hypoxic events. However, total phosphorus (TP) loading, in-lake TP concentrations, chlorophyll a (Chl a), and sediment oxygen demand (SOD) have all declined in the central basin since the 1970s. Water clarity in this basin has declined from the 1970s to 2000s despite the invasion of dreissenid mussels around 1990. In shallow lakes, declines in benthic primary production (PP) can generate positive feedback loops between the internal loading of nutrients/dissolved organic carbon and hypoxic/anoxic conditions in the water column. Such a hypoxia-inducing mechanism driven by declines in benthic PP has not been explored in Lake Erie. To test if a decline in benthic PP might explain hypoxic events in the central basin of Lake Erie, we calculated the inter-decadal changes in benthic and planktonic algal production in this basin from the 1970s to the 2000s. Primary production models using water column Chl a concentrations and light attenuation indicated that benthic PP represents roughly 10% of the basin’s total areal PP. However, our calculations show that benthic PP declined from approximately 540 to 200 g C/m2 y since the 1970s. We propose that a decline in benthic PP may have played a key mechanistic role in the transition from externally-induced hypoxia (i.e. watershed nutrient loading fueling phytoplankton production) in the 1970s and 80s to internally-induced hypoxia (sediment resuspension and internal loading) since the late 1990s.
DOI: 10.1016/j.jglr.2017.03.016 VOLUME: 43 ISSUE: 3 LENGTH: 5 pages
It Takes Two to Tango: When and Where Dual Nutrient (N & P) Reductions Are Needed to Protect Lakes and Downstream EcosystemsOHSU-RS-1573 ABSTRACT:
Preventing harmful algal blooms (HABs) is needed to protect lakes and downstream ecosystems. Traditionally, reducing phosphorus (P) inputs was the prescribed solution for lakes, based on the assumption that P universally limits HAB formation. Reduction of P inputs has decreased HABs in many lakes, but was not successful in others. Thus, the “P-only” paradigm is overgeneralized. Whole-lake experiments indicate that HABs are often stimulated more by combined P and nitrogen (N) enrichment rather than N or P alone, indicating that the dynamics of both nutrients are important for HAB control. The changing paradigm from P-only to consideration of dual nutrient control is supported by studies indicating that (1) biological N fixation cannot always meet lake ecosystem N needs, and (2) that anthropogenic N and P loading has increased dramatically in recent decades. Sediment P accumulation supports long-term internal loading, while N may escape via denitrification, leading to perpetual N deficits. Hence, controlling both N and P inputs will help control HABs in some lakes and also reduce N export to downstream N-sensitive ecosystems. Managers should consider whether balanced control of N and P will most effectively reduce HABs along the freshwater-marine continuum.
DOI: 10.1021/acs.est.6b02575 VOLUME: 50 ISSUE: 20 LENGTH: 8 pages
Oxygen use by Nitrification in the Hypolimnion and Sediments of Lake ErieOHSU-RS-1540 ABSTRACT:
Nitrification is an oxygen consumptive process, consuming 2 mol of oxygen permol of ammonium oxidized. Hypolimnion
VOLUME: 40 ISSUE: 1 LENGTH: 5 pages
Poster covering sedimentation and dredging issues in Lake Erie
Seasonal Changes in Microbial Community Structure and Activity Imply Winter Production is Linked to Summer Hypoxia in a Large LakeOHSU-RS-1566 ABSTRACT:
Carbon and nutrient cycles in large temperate lakes such as Lake Erie are primarily driven by phototrophic and heterotrophic microorganisms, although our understanding of these is often constrained to late spring through summer due to logistical constraints. During periods of > 90% ice cover in February of 2008, 2009, and 2010, we collected samples from an icebreaker for an examination of bacterial production as well as microbial community structure. In comparison with summer months (August 2002 and 2010), we tested hypotheses concerning seasonal changes in microbial community diversity and production. Bacterial production estimates were c. 2 orders of magnitude higher (volume normalized) in summer relative to winter. Our observations further demonstrate that the microbial community, including single-celled phototrophs, varied in composition between August and February. Sediment traps deployed and collected over a 3 year period (2008–2011) confirmed that carbon export was ongoing and not limiting winter production. The results support the notion that active primary producers in winter months export carbon to the sediments that is not consumed until the warmer seasons. The establishment of this linkage is a critical observation in efforts to understand the extent and severity of annual summertime formations of a zone of regional hypoxia in Lake Erie.
DOI: 10.1111/1574-6941.12238 VOLUME: 87 ISSUE: 2 LENGTH: 10 pages