Water-quality trends in suburban Houston, Texas, 1954-97, as indicated by sediment cores from Lake Houston

Abstract

Water-quality trends were assessed in Lake Houston using age-dated sediment cores. Sediments deposited in the lake contain a partial chemical signature of human activities in the watershed. Over time, a water-quality history is recorded in the bottom sediments. Although the sediments in Lake Houston are clean compared to sediment-quality guidelines, increasing concentrations of mercury, zinc, and polycyclic aromatic hydrocarbons (PAHs) during the past several decades are evidence of the increasing human effect on water quality. The positive effects of regulation are indicated by decreases in concentrations of lead and DDT. As cities grow and urban sprawl replaces rangeland, agricultural fields, and forests, water quality declines (Van Metre and others, 2000). Large numbers of people, cars and trucks, the presence of industries, and large amounts of impervious surface all contribute to the decline. Conversely, new regulations and other changes in human activities, for example, banning a pesticide or switching to unleaded gasoline, can result in improvements in water quality (Callender and Van Metre, 1997; Van Metre and others, 1997). Many of the contaminants of concern in the environment are hydrophobic (literally "water fearing") and are, therefore, mostly attached to soils and sediments. Just because they are not dissolved in water, however, doesn't mean they are not of concern. In 2001 the Agency for Toxic Substances and Disease Registry and the U.S. Environmental Protection Agency (USEPA) published a priority list of hazardous substances (Agency for Toxic Substances and Disease Registry, 2001). Fifteen of the top 20 contaminants on the list are hydrophobic, including 4 trace elements and 11 organic contaminants. One method for determining trends in hydrophobic contaminants is the chemical analysis of sediment cores. As sediments accumulate in lakes and bays, they create a partial historical record of water quality. The purpose of this study was to determine historical trends in the concentrations of selected hydrophobic contaminants in the Lake Houston watershed using sediment cores from the lake. The study was a cooperative effort between the U.S. Geological Survey (USGS) and the City of Houston. This report describes the methods of collecting and age-dating sediment cores and the resulting historical trends in hydrophobic contaminants. The report also briefly describes the results of tributary streambed sampling to help explain differences in sources of contaminants to the lake on the basis of land use. The report concludes with implications of the findings for the water quality of Lake Houston. Lake Houston is a shallow reservoir on the San Jacinto River located about 25 miles northeast of Houston, Tex. It was constructed by the City of Houston in 1954 with a maximum capacity of 146,700 acre-feet and surface area of 19.1 square miles. The drainage area for Lake Houston (fig. 1) is 2,835 square miles. The upper end of the lake splits into two arms. Tributaries to the western arm include the West Fork San Jac...

Collection, analysis, and age-dating of sediment cores from 56 U.S. lakes and reservoirs sampled by the U.S. Geological Survey, 1992-2001

“…Sediment deposition in a reservoir normally is focused into the pre-reservoir stream channel and varies along the axis of the reservoir, decreasing from the river inflow to the dam (Van Metre and others, 2001;Wilson and Van Metre, 2000). Higher sedimentation rates reduce the effects of diagenesis (Callender, 2000) and postdepositional mixing (Robbins, 1986) and improve the temporal resolution of individual core intervals.…”

“…The clearest conclusion from the comparison shown in figure 8 is that the greater the MAR, the more likely the age-dating rating was "good." This was expected because greater MAR improves temporal resolution in core samples, reduces the effects of postdepositional mixing, and reduces the effects of diagenesis (Callender, 2000), all of which increase the preservation of trends and the ability to sample them at a finer temporal resolution. MAR might be related to the watershed size as well; the rank correlation between MAR and watershed area is significant (Spearman's rho = .495; p-value <.01).…”

“…Three gravity cores were collected from three locations in the lake in July 1997: HOE (east) in the upper part of the lake on the eastern arm, HOW (west) in the upper part of the lake on the western arm, and HOS (south) in the main part of the lake near the dam. A single surficial sample, HON, was collected at a fourth site near HOS (Van Metre and Sneck-Fahrer, 2002) and was not dated.…”

Relations between hydrology, water quality, and taste-and-odor causing organisms and compounds in Lake Houston, Texas, April 2006-September 2008

“…Previous studies indicate that in general, larger loads of nutrients, suspended solids, and other water-quality constituents are contributed from the western tributaries to Lake Houston, largely because of urbanization in the western subbasin (Liscum and others, 1999;Van Metre and Sneck-Fahrer, 2002;Sneck-Fahrer and others, 2005). Lake Houston displays longitudinal gradients characteristic of reservoirs, with larger nutrient concentrations, turbidity, and algal biomass in the riverine zone (up-reservoir) of the reservoir and smaller concentrations in the lacustrine zone (down-reservoir) near the dam (Conrad, 1986;Sneck-Fahrer and others, 2005).…”

Simulation of the effects of different inflows on hydrologic conditions in Lake Houston with a three-dimensional hydrodynamic model, Houston, Texas, 2009–10

“…Specific conductance, which is an indicator of ion concentration (Hem, 1985), followed the same patterns in 2009 and 2010 observed in previous studies for nutrients, suspended solids, and other water-quality constituents. In general, larger loads of nutrients, suspended solids, and other water-quality constituents are contributed to Lake Houston from tributaries in the western watersheds than from tributaries in the eastern watersheds, reflecting the differences in land use in the watersheds (Liscum and others, 1999;Van Metre and Sneck-Fahrer, 2002;Sneck-Fahrer and others, 2005). In 2009 and 2010, the specific conductance measured at the Spring Creek gage used to represent the western watersheds was generally higher and more variable than the specific conductance measured at the East Fork San Jacinto gage used to represent the eastern watersheds ( fig.…”