Sedimentary and historical context of eutrophication and remediation in urban Lake McCarrons (Roseville, Minnesota)

Abstract

Geochemical analysis of the varved (annually laminated) sediments of a small, deep urban lake in east-central Minnesota shows that some water-quality and watershed indicators are approaching prehistoric (pre-1850s) values after an excursion to anomalous levels during the 1920s through 1950s. This high-resolution paleolimnological information (annually resolved for most of the 20th century), including varve thickness measurements on a digital image, carbon stable isotopic composition of organic matter, and sedimentary component quantification, provides historical perspective to lake managers planning remedial measures with reference to the "natural" state of the lake, especially in regard to the perception that water quality has declined only in recent decades (i.e., in the late 20th century). The lake is at present eutrophic and oligomictic, with oxygen-depleted bottom waters enriched in dissolved solids relative to surface waters; an alum treatment has contributed to the problem of persistent stratification at the same time as it has reduced phosphorus and increased transparency in lake surface waters. The sedimentary record shows the lake's strong response to agricultural, recreational, and urban development in the watershed, gradual improvement beginning at the time of sanitary sewer installation in the 1960s, and only a minor additional response to a concerted remediation effort in the mid-1980s to 1990s. Indices of terrestrial inputs and algal productivity show evidence of a lake that was at its most heavily impacted during the mid-20th century, and which has improved in some respects since the 1960s.

Identification of subannual patterns in microbial community signatures from individual sedimentary laminae using a freeze-coring approach

“…) potentially reflects expected increased diatom input to the sediment during that interval. Chloroplast enrichment in white laminae is coincident with the observation of increased proportions of diatom debris (Myrbo ). By contrast, phototrophic green sulfur bacteria and cyanobacteria exhibit no consistent difference between light and dark laminae while showing effects of degradation with increasing depth.…”

“…Lake McCarrons sediments have been continuously laminated—indicating persistent anoxia—since ∼1916 due to eutrophication primarily attributed to anthropogenic sources (Myrbo ). Light‐colored laminae from Lake McCarrons are enriched in calcite and diatom frustules generated in spring and summer blooms, while dark horizons are primarily composed of organics and fine clastic material settling out in winter (Myrbo ). Sedimentation rates in the 20th century are as high as 0.5 cm yr −1 .…”

“…Sedimentation rates in the 20th century are as high as 0.5 cm yr −1 . Lake waters were treated with copper sulfate to reduce algal levels in 1928 (Myrbo ). In fall 2004 an alum (aluminum sulfate) treatment was applied to lake waters in a successful effort to reduce water column P and internal P loading, resulting in a ∼ 4 cm horizon of amorphous aluminum hydroxide in the studied cores (samples at 6 cm and 8 cm).…”

Sulfur isotope systematics of a euxinic, low-sulfate lake: Evaluating the importance of the reservoir effect in modern and ancient oceans

“…DR1 in the GSA Data Repository 1 ). Sedimentation rate in the deepest part of the basin (17.3 m water depth) is ~0.5 cm/ yr (Myrbo, 2008). Water-column and sediment samples were collected from two locations with euxinic bottom waters: a 14-m-deep site with average values of 332 μM and 273 μM, respectively.…”

Patterns and drivers of change in organic carbon burial across a diverse landscape: Insights from 116 Minnesota lakes

“…Burial increases in ag lakes but declines in non‐ag lakes, some of which reside in catchments that underwent ag‐to‐urban conversions during this period. Although urban activities—for example, the construction and use of roads, residences, and lakeside recreation areas—can elevate sediment and nutrient yields well above natural baselines [ Engstrom et al , ; Garrison and Wakeman , ; Myrbo , ; Ramstack et al , ], it appears that they generally do not alter OC burial rates to the same extent as agricultural land uses.…”