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Investigations were preformed to better understand the influence of land use (LU) on water quality along the West Branch (WB) tributary. The WB located in Lancaster County, Pennsylvania (PA), is part of the Little Conestoga Creek Watershed (LCW). LU along the WB was assessed using Geographic Information Systems (GIS) and on-site descriptions were made at fifteen separate water sampling sites. Field study was conducted on two separate occasions; one occasion was a base-flow event and the other was considered a rain event. Water samples were collected and tested on-site for conductivity and total suspended solids (TSS) or taken to the lab for nitrate analysis. Other collected measurements included, bank height, water depth, and water temperature. During the base-flow event, the mouth of the WB extending to site seven tested extremely high for nitrate. Measurements ranged from (8.35ppm to 12.43ppm). Two drainage pipes and a tributary of the WB were also tested at base-flow; these three samples ranged from (9.5 to 15ppm). A t-test of two means showed a significant difference between the nitrate levels at base-flow and the nitrate levels during the rain event. The average recorded nitrate concentrations decreased during the rain event (p-value < 0.004); however, site eleven extending to the mouth still tested high in nitrate during the rain event (7-11ppm). A slight correlation also exists between decreasing nitrate levels and increasing forest cover (r2 = 0.27). All measurements of conductivity tested below 725 microsiemens (mS), which is within local water regulations. Regression analysis proved a positive exponential relationship between the amount of rainfall during the previous 48 hours and the amount of TSS (p-value < 0.001). TSS measured between (1.4 and 5.5 NTUs) during the base-flow event; however, the tributary and drainage pipes are responsible for all the readings above 2.0 NTUs. During the rain event TSS measurements ranged from (2.0-9.0 NTUs) while the drainage pipes and tributary ranged from (7.2-9.0 NTUs). All measurements of bank height, water depth and water temperature were inconclusive and thrown out due to their situational variability.
Land use practices and changes in south-central Pennsylvania are partially responsible for contributions of nutrients and sediments to local water sources and ultimately more distant sources, such as the Chesapeake Bay (Bay). Excess amounts of nutrients and sediments impair water quality and ultimately aquatic health. Nutrients and sediments that make their way to the Bay are regularly released into distant and local waterways through many aggregated non-point sources (NPS). It becomes a challenge to quantify how much nutrient and sediment are tied to LU in Lancaster. Research was conducted on the (WB) tributary to better understand and attempt to measure the relationship between the effects of LU on water quality. Further understanding of this relationship will help to aide future land use management decisions and ultimately help to clean up local and distant water sources.
Figure Created by Colby Landiss and Colton Brown
Research was preformed along the WB of the Little Conestoga Creek. The WB is part of the LCW and located within Lancaster. Naturally fertile soils have helped Lancaster to become one of the most agriculturally productive areas in the United States (De Wet et al., 1997). As a result, this region has experienced steady population growth and land conversion. Initially, forested lands were converted into agricultural lands and more recently these agricultural lands are being converted into urban and suburban development (Loper & Davis, 1998). A GIS map was created to better illustrate land use in the LCW as seen above in [figure- 1]. Agriculture was the most dominant type of land use in the LCW in 1998 and it accounted for 68% of the total land use, whereas 22% was urban land use, and 10% was forest cover (Loper & Davis, 1998). Today, over ten years later, it can be assumed that agriculture has decreased while suburban and urban LU have grown, but suburban more so than urban due to the enforcement of an urban growth boundary. "Changes in land use can often be associated with changes in water quality" (Stainbrook, 2006) and a previous bio-assessment study conducted by the USGS, A Snapshot Evaluation of Stream Environmental Quality in the Little Conestoga Creek Basin, Lancaster County, Pennsylvania, indicated that almost the whole watershed is impaired (Loper & Davis, 1998).
High nutrient and sediment concentrations negatively impact water quality and ultimately life in and around the Bay. Nutrients and sediments enter waterways through many sources. High concentrations of nutrients act as a catalyst for algal growth and foster hypoxic environments. Excess amounts of sediments can cloud water and starve aquatic plants and animals of sunlight. Both circumstances act as stimulants for forming algal blooms, which lead to devastating losses of plant and animal life; also known as eutrophication. In a previous bio-assessment study, referenced in the USGS Snapshot Article, it was determined that nutrient levels were frequently above 10mg/L within the lower part of the WB, which is dominated by agricultural LU (Loper & Davis, 1998).
The LCW is not only a source of nutrients, but also the highest producer of sediment to the Conestoga River, the Susquehanna River, and the Chesapeake Bay (Hubbard, 2006). It is hard to measure exactly how much and where nutrients and sediments are coming from, because unlike point sources (PS), such as a drainage pipe from a sewage treatment facility, the bulk of pollutants in this watershed are coming from many aggregated NPS.
Historically, it is understood that 50% of sediment erosion from the LCW is related to stream bank erosion (Walter, 2006). This is a major issue in the LCW because many local streams were at one point dammed and used for grinding grain, gunpowder, and sawing lumber. These dams created slack water ponds behind them that collected sediment and nutrients runoff from farmlands over many years. When technologies advanced the dams were deconstructed releasing hundreds of years of built up sediments and nutrients into local waterways, which drain into the Conestoga River, the Susquehanna River, and ultimately the Bay. Geochemical studies reveal that these bank sediments contain 1500-3000ppm of nitrogen and 400-800ppm of phosphorus (Walter, 2006).
In a previous study, Remote Sensing of Land Use Cover Factors Influencing Soil Erosion in the Little Conestoga Watershed, Lancaster County, Pennsylvania, exported sediment from the LCW was measured using remote sensing imagery in conjunction with rainfall data collected from April 2000 to October 2005. The authors determined that periods of highest turbidity in the Lower Susquehanna River and Upper Chesapeake Bay correlate with periods of high bare ground cover and heavy rainfall events in the LCW. Rates of sediment export are naturally higher during the agricultural off- season (Sep-May), especially during rain events such as spring snow melt and tropical rain storms (Hubbard, 2006).
The LCW has been studied for over twenty years. The causes of poor water quality and the scope of the issue are well known, but there is limited data to solidify the relationship between land use change and water quality degradation. Research was preformed to re-investigate the relationship between land use and water quality in the West Branch (WB) of the Little Conestoga Creek during April 2011.
In order to further research the relationship between land use and water quality in the WB, water samples were collected beginning from the mouth of the WB and ending at the head waters. Sampling sites were chosen based on a perceived change in land use along the way. At each sampling site, three samples were collected in an upstream fashion and both tested on site and filtered and tested later in a laboratory. Beyond just sampling the water, land use and Best Management Plan (BMP) assessments were made using photography, journal entry, and a Garmin GPS device was used to mark each sampling site.
On-site Testing: Testing that was preformed on-site included tests such as, conductivity measured using a LaMotte Pocket Tester Kit in mS (microsiemens), Total Suspended Solids (TSS) measured using a LaMotte colorimeter in NTUs (Nephelometric- Turbidity Units), and water temperature was measured using the Pocket Tester in degrees Celsius. Other measurements that were taken included bank height and water depth, both were measured in centimeters. All sample bottles were previously cleaned and all instruments were calibrated prior to sampling.
Conductivity: A measurement of the total amount of dissolved organic and inorganic compounds in the water sample, also known as a measurement of conductivity due to the presence of ions. Some of these dissolved compounds could include calcium, sodium, nitrates, phosphates, and potassium.
Conductivity sample analysis steps: The LaMotte Pocket Tester was set to measure conductivity and inserted into each sample bottle for thirty seconds to one minute. Once the measurement leveled off the number was recorded in microsiemens.
TSS: A measurement of the total amount of suspended solids of the water sample. Measurements are based on how cloudy or hazy each sample is when compared to the calibrated water sample that is perfectly clear. Excess sediments can cloud the water and larger compounds such as phosphates stick to these sediments and further harm water quality.
TSS sample analysis steps: Each sample was poured into a glass vial and placed into the colorimeter. The colorimeter was pre-calibrated to ten NTUs using a controlled solution and each sample received its value based off this calibration and recorded in NTUs.
Bank height: A measurement of the height of creek bank at each sampling site related to the height of the water level using a meter stick at each sampling site. This measure could have potentially related to high measurements of turbidity and conductivity.
Water depth: A measurement of the depth of water at each sampling site recorded using the meter stick and placed in the middle of each stream. This measure could have potentially provided a comparison of base flow vs. storm flow.
Off-site testing: Samples that were collected for nitrate analysis were filtered and chilled on site in a cooler to prevent bacterial growth. Later, each sample was analyzed in the laboratory using a colorimeter and measured in parts per million (ppm).
Nitrate analysis steps:
Because the colorimeter only reads up to 3ppm the water samples had to be diluted with clean water and a mixed acid reagent
The sample was caped, mixed, and sat for two minutes
Cadmium powder was then added to each diluted sample, shook for four minutes, and then sat for ten minutes
Each sample was then placed in the colorimeter and if the reading was over range, then the sample was diluted once more
TSS: On the baseflow day only the sites ranging from the mouth to site seven were sampled including one tributary at site three and two drainage pipes at site seven. The drainage pipes and tributary were responsible for the highest readings ranging from 2.0-5.5 NTUs while all other sites on average ranged from 1.4-2.0 NTUs.
Figure created by Colton Brown Brown
During the rain event the sites ranging from the mouth to site nine were tested excluding site two and including the two drainage pipes and tributary. The drainage pipes were responsible once again for the highest reading ranging from 7.2-9.0NTUs and the
Tributary measured at 7.2NTU. All other sites ranged from 2.0-6.8NTU. Regression analysis as shown above in [figure 2] proved a positive exponential relationship between the amount of rainfall during the previous 48 hours and the amount of total suspended solids (p-value < 0.001). On average the amount of TSS increased with rainfall and decreased during baseflow.
Conductivity: The maximum allowed conductivity for waters in the Conestoga River are 800 microsiemens. All measurements of conductivity on average were below 725mS. No relationship exists between measurements of conductivity during the base flow event compared to the rain event.
Nitrate Analysis: The base flow event nitrate samples extending from the mouth to site seven ranged from 8-12ppm. The tributary at site three and the two drainage pipes at site five ranged from 9-15ppm.
The rain event samples extended from upstream of the mouth of the WB on the Little Conestoga Creek to site 15 and ranged from 2-11ppm. The tributary and drainage pipes ranged from 4-10ppm.
Figure created by Colton Brown
A t-test of two means showed a significant difference between the nitrate levels at base-flow and the levels during the rain event. The average recorded nitrate concentrations decreased during the rain event (p-value < 0.004). Site eleven extending to the mouth still tested high in nitrate during the rain event (7-11ppm). [Figure 3] above and to the left provides a clear illustration of nitrate values taken at base flow compared to values measured during the rain event. A slight correlation also exists between decreasing nitrate levels and increasing forest cover (r2 = 0.27).
All measurements of bank height, water temperature, and water depth were disregarded because they were too varied and became somewhat meaningless figures.
Figure by Colby Landiss and Colton Brown
More than 50% of the land along the WB is agriculture. Agriculture extends from the mouth to the head waters. Because there is little variation in LU along the WB there is also little room for comparison to other types of LU. A correlation cannot be drawn between LU and nutrient or sediment pollution. However, the water is seriously impaired at multiple locations and this is illustrated in the graduated symbols map illustrated by [figure- 4]. This map tells us that a relationship does exist between rain and dilution of nitrate in the WB. The more rain there is the less nitrate there appears to be. If water samples were taken after the rain had a chance to settle there might be higher concentration than seen during base-flow. The largest amount of varaition was found between site twelve and site eleven. Site eleven was actually a tributary to the WB, but it was believed to be part of the WB at the time of sampling. If there was be futher study this would be a good place to preform more research because site eleven drains directly from an agricultural field. Determining the cause of the nitrate spike could be the first step towards pollution mitigation.
Discovering the relationship between increased rainfall and increased amounts of TSS was not suprising; however, the colorimeter became uncalibrated during the rain event from site ten through site fifteen, but this should not affect the percieved relationship. Stormflow and flood events are known vehicles for sediment and nutrient. Storm flow can cut away at stream banks which could potentially hold legacy sediments and wash fertilizers from lawns and agricultural fields into local and distant waterways.
NPS pollution impairs water quality and disturbs aquatic ecosystems (Walter& Oakes, 2007). Excessive inputs of nutrients and sediments result in eutrophication and consequentially alter the trophic states of freshwater. The nature of water is to drain into larger bodies and some percentage of water in the LCW ultimately finds its way into the Bay. Because, "Land use drives nutrient loadings throughout the United States and elsewhere" (Walter & Oakes) appropriate land management is necessary to protect not only local environments, but also further environments, such as the Bay.
Installment of BMPs is an important part of successful land management. Land use assessments were made along the WB and little to no buffers existed. There were some natural forested areas near the mouth and along the banks, but for the most part the WB is un-buffered. It was previously shown that an increase in forest cover leads to a decrease in nitrate. Federal grant money exists to assist farmers with the expenses of planting buffers as well as creating nutrient management plans. If Lancaster intends to help clean up their local waterways as well as the bay they are going to need to employ a variety of BMPs and educate those who wish to make a difference.