Landuse effects on Nitrate and Ammonia

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Land-use Effects on Nitrate and Ammonia Concentrations

Introduction

Nitrogen plays an important role in global environmental cycles. Its most important environmental function is acting as a limiting nutrient in brackish and saltwater ecosystems. It is also an essential element to many biological processes including the function of amino acids, proteins, and nucleic acids (http://www.water.ncsu.edu/watershedss/info/no3.html). Nitrogen, like many other elements, follows a basic cycle through the environment. Its journey begins in the atmosphere, which is made up of approximately 78% nitrogen. However, organisms are not able to utilize it in its inorganic gaseous form. It must first be converted to an organic form, either nitrate or ammonia, which is accomplished by bacteria that reside in soil. Once nitrification and nitrogen fixation have taken place, the organic forms of the element can be actively taken up by plants, and be passed up the food chain. Nitrates are converted back to inorganic nitrogen and returned to the atmosphere by a process called denitrification, which is carried out by bacteria under anaerobic conditions (http://en.wikipedia.org/wiki/nitrogen_cycle). The environmental effects of excessive nitrate and ammonia can be devastating to estuarine and saltwater ecosystems, in which nitrogen is the limiting nutrient. Increased levels of nitrate and ammonia can increase the primary productivity of an ecosystem, leading to algal blooms and high rates of aquatic plant growth. Large algae blooms are detrimental to biodiversity in an ecosystem. They block sunlight from reaching other aquatic plants, reducing photosynthesis and eventually killing underlying plants. Eutrophication of the waterway may occur due to the decomposition of dead algae. Dissolved oxygen levels this low cannot support the needs of fish or other aquatic organisms, and as a result, areas of the body of water affected may become “dead zones”. Some species of algae can also release toxins into the water, killing any wildlife present (http://www.water.ncsu.edu/watershedss/info/no3.html). Nitrates are difficult and costly to remove from bodies of water, and it is often difficult to determine definite sources of nitrate and ammonia to the environment. Point sources include industries that use nitrates to manufacture their products. For example, nitrates and ammonia are often used to produce fertilizer and explosives, and to manufacture glass and solar heating appliances. Non-point sources include runoff containing fertilizers and livestock excrement from farmland, as well as lawn fertilizers, leaky septic tanks, combustion of fossil fuels, and wildlife excrement (www.ncsu.edu/watershedss/info/no3.html).

Hypothesis

We expect to see a relationship between nitrate and ammonia concentrations and the type of land-use and anthropogenic influences in that area. We also expect that the concentrations will vary predictably depending on the salinity and pH of the water being measured.

Methods:

In this study the process of our data collection began with direct sampling from predetermined sites. These sites were selected by their accessibility and expected differences in salinity, H+ concentration, nitrate, and ammonia concentration. The exact sites sampled in this study are listed as follows: (1) A fuel dock adjacent to current construction, at a marina behind Dockside Restaurant. (2) A public boat launch near the Lesner Bridge. (3) A polluted drainage ditch behind a residential area. (4) A private boat dock in a housing development. (5) Great Neck Bridge. (6) Pretty Lake. (7) A duck feeding pond. (8) Lake Whitehurst. (9) Lake Smith. (10) An un-named lake near Chicks Beach. (11) Broad Bay. (12) A cypress bog in First Landing state park. (13) Lake Taylor. Sampling of these sites was conducted on two separate days; samples 1 through 5 were collected on April 6, 2005, while samples 6 through 13 were collected on April 14, 2005. At each site approximately 60 ml of water was collected with an extendable sampling rod. The samples were then bottled, labeled, and placed on ice to inhibit any chemical changes that may be caused by a raise in temperature. In addition to the samples themselves, a few other types of data were collected at each site. A GPS unit was used to record the exact UTM coordinates of each site. Also, digital photos were taken for visual documentation, and a description of the area was recorded for aid in the determination of land-use categories (see Appendix for photos). Those descriptions also included notes on obvious factors surrounding each site that may have an effect on our measurements. We expected some of theses factors to be things like species of plant life, proximity to major roads, or visible pollution in the water. Back in the lab all samples were tested for salinity, H+ concentration, nitrate, and ammonia concentration. Salinity was determined in parts per thousand by using a refractometer calibrated with distilled water. H+ concentration was determined by using a pH probe to obtain an initial pH reading and applying an equation to that reading to determine its negative log. Nitrate and ammonia concentrations were determined using the method outlined in the Lamott water quality analysis kit. Replicate samples were taken and analyzed for nitrate and ammonia concentration. The sites where replicate samples were taken and analyzed included the duck feeding pond and Broad Bay. All data was then entered into an Excel spreadsheet. Columns were then added to show land use category and anthropogenic influence. The land use was listed in code numbers as follows: (1) Construction. (2) Residential (3) Recreational (4) State Protected. The level of anthropogenic influence was also listed in code numbers: (1) More anthropogenically influenced and (2) Less anthropogenically influenced. This data was then used to make multiple graphs showing concentration and linear regressions were conducted to look for relationships between readings. We looked for correlations between salinity and H+ concentration, salinity and nitrate, and nitrate and ammonia (see Appendix for graphs). For spatial analysis a GIS map was compiled. This was done to visually display the extent of our sampling and allow for a better understanding of the proximity of our sample sites in relation to the Atlantic Ocean and the Chesapeake Bay. This was also useful in determining the type of land use around the sites. The map was created starting with a topographic base map. After the base map was created, nine digital ortho-rectified quarter quadrangles were added, and individual spatial data were set to align the aerial photographs over the base map. Using the UTM coordinates we obtained from the GPS unit in the field, we entered them into the GIS program to display the x,y data points on the map.

Results

Only three of the thirteen samples, numbers 6, 10, and 13, produced results for nitrate, ranging in value from 0.02 to 0.16 ppm. All three of the samples had intermediate levels of ammonia, ranging 0.01 through 0.17 ppm, had pH readings around 7, and were all from residential areas with anthropogenic influence ratings of 1. Ammonia readings ranged from 0-1.61 ppm. The three highest samples, numbers 3, 4, and 5, were all below detection limit for nitrate, had pH’s ranging from 7.25-8.2, and were all in anthropogenically-influenced areas (see Appendix Table 1). By using a graph and a linear regression, we determined that pH increased with salinity. Beyond this, we were unable to demonstrate any relationship between any of the other factors (see Appendix for graphs).

Discussion

The results that we obtained did not support our original hypothesis. We were unable to establish any correlation between nitrate and ammonia concentrations and land-use. We believe that this may be due to the number of factors that affect the influx of nitrates and ammonia to a watershed. In a revised study, we speculate that we would possibly take more samples at a smaller number of sites at pre-determined intervals over the course of a year to determine if there were seasonal patterns of nitrate and ammonia deposition to certain bodies of water. From that information, we would also be able to ascertain whether or not possible correlations existed between pH and salinity, and ammonia and nitrate deposition at those locations. Once this information was considered, we could begin to look at possible sources of ammonia and nitrate, and determine what role, if any, land-use possibly would play in ammonia and nitrate deposition. We believe that the low values of nitrate and ammonia could be due to the season in which sampling was conducted. We had expected to have higher concentrations in the residential areas due to lawn and garden fertilizer; however, it is possible that little or no fertilizer had been applied to lawns and gardens in those areas that early in the year. We also expected nitrate levels to be high in the duck-feeding pond due to the presence of so many birds. However, there was abundant vegetation growing in and around the water, so we believe that these plants may be using the nitrate for some sort of biologic function. Ammonia and nitrate are both important constituents of the nitrogen cycle, and their effects on aquatic ecosystems have been widely studied. In a survey conducted on alpine lakes in the High Tatra and Sumava Mountains in Europe, researchers determined that a high ratio of total nitrogen to total phosphorous indicated that nitrogen was not a limiting nutrient in freshwater ecosystems. While high levels of nitrate and ammonia do not increase primary production in freshwater ecosystems, they are the limiting nutrients for marine and estuarine ecosystems. High concentrations of the two constituents in saltwater can result in large algal blooms, which can lead to eutrophication of the system (Kopacek et al, 1995). This knowledge may be used for future studies to determine whether the phytoplankton populations in estuarine and marine systems are utilizing ammonia and nitrate, and are the reasons why we did not have higher concentrations. The researchers also looked at the acidifying effects of nitrate in surface water. They found that high concentrations of nitrate resulted in low pH levels (Kopacek et al, 1995). However, our data did not reflect the same trends, as most of our nitrate readings were from sample with a pH around 7. The uncertainty in our data may be due to the large quantity of factors affecting the concentrations of ammonia and nitrate at the sample sites. Seasonal variations of ammonia and nitrate concentrations may also be related to the amount of rain an area recently had. While we originally decided that rainfall would decrease concentrations in the water, a study conducted by Menzel and Spaeth (1962) suggested otherwise. They found that ammonia concentrations were much higher after precipitation events, which were more common in warmer months. After studying their data, they noticed that ammonia concentrations were always higher than nitrate concentrations. They speculated that ammonia may build up in an ecosystem because it is not being used by organisms as quickly as nitrate. Our ammonia concentrations were all larger than our nitrate readings, which may be explained by Menzel and Spaeth’s theory. Another possible source of uncertainty could be the seasonal variations of land-use in the areas of testing. Perhaps people had not put fertilizers down that early in the year. Or perhaps no rain had fallen for a few days, which would decrease run-off to the bodies of water. It is also possible that there is a local plant or organism that is utilizing nitrate faster than ammonia. However, we find this unlikely due to the fact that we tested both freshwater and saltwater ecosystems, and that not many organisms can survive in both types of water. Future studies may compare ammonia and nitrate concentrations between marine and freshwater ecosystems, to study the effects that phytoplankton have on the relative concentrations of both constituents. Another possible study could look at ammonia levels in precipitation to determine if it is a large source of ammonia to an ecosystem. Once other possible sources are quantified, it may be easier to determine what role land-use plays in the addition of ammonia and nitrate to an ecosystem.

References:

Kopacek, J., Prochazkova, L., Stuchlik, E., Blazka, P., 1995. The Nitrogen-Phosphorous relationship in Mountain Lakes: Influence of Atmospheric Input, Watershed, and pH. Limnology and Oceanography 40, 930-937. Menzel, D.W., Spaeth, J.P., 1962. Occurrence of Ammonia in Sargasso Sea Waters and in Rain Water at Bermuda. Limnology and Oceanography 7, 159-162 http://en.wikipedia.org/wiki/Nitrogen_cycle http://www.water.ncsu.edu/watershedss/info/no3.html GIS Data http://www.radford.edu/~geoserve/doqq/doqq_va_1_01.htm http://fisher.lib.virginia.edu/collections/gis/doq/helps/doqq_meta.html http://data.geocomm.com/catalog/US/61083/1828/group129-3.html http://www.digital-topo-maps.com/virginia.shtml http://www.esri.com http://www.noaa.com

Appendix Contents:

Sample sites
Photographs of sample sites

Graphs:
Salinity vs. NO3_NH3
Salinity vs. pH
Land-use vs. NH3
Land-use vs. NO3
Land-use vs. pH
PH vs. Anthropogenic Rating
Anthropogenic Rating vs. NH3
Anthropogenic Rating vs. NO3

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