Nitrate in the Freshwater Fish tank

Introduction

Nitrates in surface water primarily result from the decay of autotrophs and from chemoheterotrophic life, for nitrates are a byproduct of the waste produced from the consumption of organic molecules as an energy source. Fish are the primary chemoheterotrophs in aquatic ecosystems; therefore, they are accountable for the majority of nitrogen found in water. Ammonia is the main component of fish waste, which is a very toxic compound of nitrogen, but aerobic ammonia oxidizers convert ammonia to nitrite via the intermediate hydroxylamine, which requires aid from ammonia monooxygenase and hydroxylamine dehydrogenase (1). Nitrite is an even more toxic form of nitrogen, but this is further oxidized to nitrate via another type of nitrogen bacteria with the enzyme nitrite oxidoreductase(1).In nature, nitrates are regulated to a certain extent through aquatic plant life, for it is essential in the production of chlorophyll (2). In fish tanks, however, algae is the only natural nitrate regulator, but unlike more complex and nutrient dependent plants, algae is able to grow beyond the capacity of a given ecosystem with ease. Algae cannot convert nitrogen to a gas that can escape the system, so when it dies, nitrogen is released back into the system (2). In closed systems, like that of a fish tank, mechanical work such as changing out volumes of water, being mindful in not overfeeding the fish, and cleaning off the algae and filtration systems, is required in order to ensure nitrate levels are kept at a safe and constant concentration. This experiment aimed to quantify the sources of nitrate in a closed off fish tank system by way of using the Thermo Fisher Scientific^TM Dionex^TM Aquion^TM Ion Chromatography System with the built in Chromeleon 7 Chromatography Data System software. While there are no direct regulations published by the EPA for nitrate and nitrite levels in a fish tank, this experiment utilized the EPA's recommendations for surface water systems. The EPA has set different guidelines for surface water that is just a reservoir for aquatic life and water that is used for human consumption. The maximum contaminant level for nitrates and nitrites in drinking water in the U.S.A. are 10.0 ppm and 1.0 ppm respectively (3). For water systems not being used as drinking water or connected to..., such as isolated ponds, the EPA recommends that nitrate levels do not exceed 60 ppm and that nitrite levels should be kept as close to 0.0 ppm as possible (3).

With a focus on nitrates and nitrites, chloride and sulfate concentrations were also investigated in this experiment. To serve as a comparative analysis, freshwater samples from a connected creek and pond system and ground water samples from a closed off underground spring were also run on the Ion Chromatographer. The EPA defined the maximum Contaminant level for chloride in drinking water as 250 ppm and interprets chlorides as chronically toxic to freshwater aquatic life at 230 ppm and acutely toxic at 860 ppm.

Materials and Methods

Fish Tank Set-Up

The closed system for which data was collected consisted of a 39 gallon freshwater fish tank with convict cichlids. An Aquatop Canister Filter was connected to the fish tank via... A feeding mechanism with the Zacro Automated Fish Feeder was devised so that 1.0 gram of TetraCichlid Floating Cichlid Pellets would be delivered twice a day. This was done by setting the automated fish feeder to release 1 meal portion at 8:30 and 16:30

Fish Tank Samples

In order to see how mainly nitrate and nitrite levels change from day to day with evaporation in a closed system, five water samples were collected throughout the week at roughly the same time each day (14:00), without adding water to the system. After a one in two dilution, these samples were then run on the Thermo Fisher Scientific^TM Dionex^TM Aquion^TM Ion Chromatography System with the built in Chromeleon 7 Chromatography Data System software, with nitrate, nitrite, chloride, and sulfate calibration standards of 5, 10, 20, 80, and 100 ppm.

To quantify eliminate nitrate concentration increments due to evaporation, a water top off system was put to use in which a float water level sensor was used to ensure the water level did not fall above or below the 29 gallon mark. Samples throughout the week were collected at the same time each day and run on the same Ion Chromatography system after performing a one in two dilution to be in range of the 5, 10, 40 and 100 ppm nitrate, nitrite, sulfate, and chloride calibration standards.

Fish Food Analysis

In order to see how much nitrate entered the system directly from the food source being supplied to the tank, a portion size of 1 gram of the TetraCichlid Floating Cichlid Pellets was diluted in 1 L of milipore water, centrifuged for 5 minutes at 300 RPM and analyzed on the ion chromatographer with the same standards as the evaporative fish tank samples were.

Pond and Creek Water Samples

Freshwater samples from a creek and a pond were collected from the locations displayed in figure 1. After a one in five dilution, they were analyzed on the same Ion Chromatography System as the fish tank samples, with nitrate, nitrite, chloride, and sulfate standards of 10, 40, and 100 ppm.

Figure 1. The red tag displays where the pond sample was collected and the gray tag shows where the creek sample was collected during late September

Ground Water Samples

A water sample from a private well that draws directly from a natural underground spring was collected along with a sample from the well source ran through a water softener.

Results

Fish Tank System

Figure 3: The data here relates nitrate increments due to evaporation, metabolic activity of the fish, and algae modulation (blue line). The rate of daily nitrate increments was determined to be 2.5912 ppm/day. A model of what the daily nitrate concentrations would be if the system were to lose 0.45322 gallons per day is modeled with the orange line and appears to be a good fit for the collected data. The modeled rate of nitrate increments was determined to be 2.6352 ppm/day.

Ground and Surface Water Analysis

Discussion

Though natural regulation proves to be useful in open surface water systems, there are a lot more variables in how nitrates and nitrites can enter the system, therefore, . Although mainly byproducts from aquatic life, nitrate and nitrite levels in surface and ground water can also result from agricultural runoff (fertilizers), improper disposal of human and animal waste, and...() While the creek and water samples collected came from a reservoir for aquatic life, it is likely the nitrate levels are also a result from the heavy agricultural activity surrounding the open system. Even so, the nitrate and nitrite levels are well below the EPA's guidelines for surface water not serving the purpose as drinking water. Road-salt runoff, which primarily consists of NaCl, can pose a major threat to surface water quality and aquatic life. Even in warm weather months, when roads are not being salted, chloride levels from winter salt applications persisted in a study carried out in Milwaukee Massachusetts (1).

References

1. Harms, G.; Layton, A. C.; Dionsi, H. M.; Gregory, I. R.; Garrett, V. M.; Hawkins, S. A.; Robinson, K. G.; Slayer, G. S. Real-Time PCR Quantification of Nitrifying Bacteria in a Municipal Wastewater Treatment Plant. Am. Chem. Soc. 2002, 37, 343-351.

2.

3. U.S. Environmental Protection Agency. https://www.epa.gov/

4. Corsi, S. R.; Graczyk, D. J.; Geis, S. W.; Booth, N. L.; Richards, K. D. A Fresh Look at Road Salt: Aquatic Toxicity and Water-Quality Impacts on Local, Regional, and National Scales. Environmental Science & Technology. 2010, 44, 7376-7382.