A Land-Use and Water-Quality History of White Rock Lake Reservoir, Dallas, Texas, Based on Paleolimnological Analyses

View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by DigitalCommons@University of Nebraska University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln USGS Staff -- Published Research US Geological Survey 1997 A Land-Use and Water-Quality History of White Rock Lake Reservoir, Dallas, Texas, Based on Paleolimnological Analyses J. Platt Bradbury USGS Peter C. Van Metre USGS Follow this and additional works at: https://digitalcommons.unl.edu/usgsstaffpub Part of the Earth Sciences Commons Bradbury, J. Platt and Van Metre, Peter C., "A Land-Use and Water-Quality History of White Rock Lake Reservoir, Dallas, Texas, Based on Paleolimnological Analyses" (1997). USGS Staff -- Published Research. 257. https://digitalcommons.unl.edu/usgsstaffpub/257 This Article is brought to you for free and open access by the US Geological Survey at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in USGS Staff -- Published Research by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. Journal of Paleolimnology 17: 227±237, 1997. 227 c 1997 Kluwer Academic Publishers. Printed in Belgium. A land-use and water-quality history of White Rock Lake reservoir, Dallas, Texas, based on paleolimnological analyses J. Platt Bradbury1 & Peter C. Van Metre2 1U.S. Geological Survey, Box 25046 MS 919 Federal Center, Denver, CO 80225, USA 2U.S. Geological Survey, Austin, TX 78754, USA Received 21 November 1995; accepted 14 March 1996 Key words: diatoms, pollen, sediment, reservoir limnology, land-use change, Texas Abstract White Rock Lake reservoir in Dallas, Texas contains a 150-cm sediment record of silty clay that documents land-use changes since its construction in 1912. Pollen analysis corroborates historical evidence that between 1912 and 1950 the watershed was primarily agricultural. Land disturbance by plowing coupled with strong and variable spring precipitation caused large amounts of sediment to enter the lake during this period. Diatoms were not preserved at this time probably because of low productivity compared to diatom dissolution by warm, alkaline water prior to burial in the sediments. After 1956, the watershed became progressively urbanized. Erosion decreased, land stabilized, and pollen of riparian trees increased as the lake water became somewhat less turbid. By 1986 the sediment record indicates that diatom productivity had increased beyond rates of diatom destruction. Neither increased nutrients nor reduced pesticides can account for increased diatom productivity, but grain size studies imply that before 1986 diatoms were light limited by high levels of turbidity. This study documents how reservoirs may relate to land-use practices and how watershed management could extend reservoir life and improve water quality. Introduction water quality has a long history and an active future (Davis, 1990). Documentation of trends in historical surface-water This paper presents pollen, diatom and grain-size quality for trace metals, pesticides and nutrient levels analyses on a 1.5-m core from White Rock Lake, a is an important facet of the National Water Quality reservoir ®rst ®lled in 1912 on White Rock Creek Assessment (NAWQA) program of the U.S. Geolo- when the drainage was largely agricultural (Figure 1). gical Survey. Understanding of the relation between Presently the creek and reservoir are surrounded by water quality and the kind and intensity of land-use suburban expansion of Dallas, Texas. In the core from practices, both agricultural and urban,will enable plan- White Rock Lake, pollen stratigraphy tracks changing ners and municipalities to avoid destructive practices land-use practices. Diatoms are only present in the that jeopardize the quality of water resources. Because upper 15 cm of the core, apparently re¯ecting increased relevant historical data (monitored water analyses) for water clarity as a result of urbanization and integrated many lakes, reservoirs and streams are lacking, or con- storm sewerage as well as decreasing agricultural activ- ®ned to comparatively recent time, paleolimnological ity in the drainage. With increased transparency, diat- and paleoecological analyses of sediment cores can om productivity in White Rock Lake could exceed rates help track changes in water quality and land-use prac- of diatom destruction by solution during and after sed- tices over the life of a reservoir or lake. The sediment imentation. core/paleo-environmental approach for documenting both natural and anthropogenic changes in lake basins, their drainages, and regional (climatic) in¯uences on Article: JOPL 370, Grafikon: 201021404, Pips nr. 113450 BIO2KAP *113450* jopl370.tex; 24/06/1997; 8:28; v.5; p.1 228 Figure 1. Index map of White Rock Lake and its urban drainage basin. Setting in 24 h may characterize thunderstorms in the spring or fall. Climate Land use and vegetation The climate of northeastern Texas is temperate with short and usually mild winters. Mean winter temperat- Native vegetation of the region is `blackland' tall-grass ures are above freezing, although in exceptionally cold prairie with woody vegetation, characterized by Carya years reservoirs in the area freeze for short periods [pecan], Salix [willow] and Ulmus [elm] growing prin- (Cole, 1963; Harris & Silvey, 1940). Mean summer cipally along streams and drainages with many other temperatures exceed 28 C and account for strati®ca- taxa. On shallow soils of the uplands, where damage tion of deeper reservoir lakes. from erosion (post cultivation) has been severe, Juni- Most precipitation falls as rain, chie¯y in the spring, perus virginiana [eastern redcedar] and annual and per- but the mean for any season is above 15 cm. Precipit- ennial weeds (chie¯y plant families of Asteraceae and ation of wet and dry years varied by a factor of three Chenopodiaceae + Amaranthaceae) become common over a 49-year period. Intense precipitation of >15 cm (Marshall & Brown, 1939). jopl370.tex; 24/06/1997; 8:28; v.5; p.2 229 Agriculture dominated land use when the reser- show considerable variability (Figure 2), but only sus- voir was constructed in 1912. Cotton and grass crops pended solids and nitrate have consistently fallen to prevailed and the rich soils required no fertilization. comparatively low values since the early 1980s. Nevertheless, soil conservation practices were uncom- In April, 1939, the diatom Melosira ( = Aulaco- mon, and accelerated soil erosion had affected 93% of seira) was recorded as the most abundant phytoplank- the land in the watershed by 1939. Catastrophic sheet ter (1741 cells L1). Nevertheless, these population ¯ooding and soil erosion through croplands after high numbers were quite low in comparison to counts of the intensity rain storms are photographically documented same genus from nearby reservoirs (Patterson, 1942). by Marshall & Brown (1939). A sample of reservoir water taken during coring in early Intensive urban development of the White Rock July, 1994 contained several diatom species, chie¯y Creek area followed World War II (1945). In 1956 Cyclotella stelligera, and smaller numbers of Synedra 14% of the drainage was urban (Zodin et al., 1971). acus, S. tenera, Aulacoseira alpigena, A. granulata, By the 1960s much of the lower drainage to the reser- and A. ambigua. voir was urban and by 1990, 72% of the 259 km2 creek drainage had been urbanized (Samuel Brush, North Central Texas Council of Governments, written com- Materials and methods munication, 1992). Coring and sampling Limnology A 6.3-cm diameter gravity core was taken from a pon- White Rock Lake is located in the suburban community toon boat/coring platform anchored in about 5 m water of Highland Park within the metropolitan area of Dal- depth in the southern third of White Rock Lake in July, las, Texas. The reservoir was ®lled in 1912 after a 1994 (Figure 1). The core was extruded and scraped 12-m dam was constructed across White Rock Creek, clean, and samples were extracted and sealed in air- a tributary of the Trinity River presumably named tight plastic bags in the ®eld. for its course across the white Austin Chalk Form- ation (Cretaceous) that outcrops along its drainage. Pollen analyses The reservoir had an area of 465 ha in 1935 after silt deposition and delta formation upstream had reduced Pollen samples were prepared by removal of carbon- the original (1912) area by about 7%. In the ®rst 25 ates with 10% HCl, silicates with 48% HF and labile years, silt had reduced the reservoir capacity by nearly organic matter with hot, 5% KOH and acetolysis (Fae- 1% per year (Marshall & Brown, 1939). Its maximum gri & Iversen, 1964). Pollen types enumerated are depth in 1939 was about 10 m (Patterson, 1942), while presented as percentages based on the count sum (usu- today the deepest part of the lake is about 6 m. Clearly ally 200) except in two cases (81 and 142 cm) where sediment accumulation rates for the basin are high. insuf®cient pollen was recovered to calculate statistic- Today, White Rock Lake is shallow, turbid and ally reliable percentages. In these cases, an arti®cial probably polymictic, completely circulating at inter- divisor of 200 was used to under-weight these pollen vals throughout the year when winds are suf®cient to spectra values graphically relative to the other samples. mix the lake. Earlier in its history when the lake was The `percentages' of these two samples do not, there- deeper, however, limnological observations indicate fore sum to 100%. transient strati®cation and hypolimnetic oxygen deple- tion in summer beneath a 4 to 9-m thick thermocline Diatom analyses (Patterson, 1942). At that time, surface water temper- ature ranged from 8.8 C in February to 28.5 CinJuly. Samples prepared for diatoms were digested in concen- pH (determined colorimetrically with a Hellige com- trated HNO3 at 100 C for 0.5 h and cleaned of remain- parometer) varied between 8.3 and 7.2 with an average ing acid and solutes by centrifugation and decantation.

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