Lake Mead Zooplankton: Studying the Impact of Climate Change - Research Paper

Lake Mead has shown constant, predictable patterns in its zooplankton population, even in the face of stressors like invasive species and drought. Being America's largest reservoir by volume (Davies & Keith 15), its patterns offer an opportunity to study the possible impacts of future climate changes. The demand for water in Lake Mead has been rising since 2007, and this adds to the increase in invasive species like quagga mussels and gizzard shads and increasing human population around the lake. Humans lead to more treated water and waste inflow into the lake, which can potentially interfere with their population dynamics. This paper describes the survival of planktons in the lake, their potential threats, and survival mechanisms.

Is your time best spent reading someone else’s essay? Get a 100% original essay FROM A CERTIFIED WRITER!

Save 25%

Located along the Colorado River, Lake Mead is a human-made lake in Nevada-Arizona, USA. It was formed when Hoover Dam was built in 1935 and supplies Nevada, some parts of Mexico, California, and Arizona with water (Baker 12). The lake is 112 miles long, 162 meters deep, and can hold up to 26 million-acre feet of water at full capacity.

Since 1983, increased water demand and drought have reduced the water volumes at the lake, making it operate at just 40% capacity by 2019 (Baker 15). Like any natural water ecosystem, Lake Mead has plankton: small plants and animals that float along the lake's currents. The little animals are called zooplankton, while the plants are phytoplankton.

Phytoplankton photosynthesize their own food while zooplankton feed on the phytoplankton. Some plankton later grow to become adult plants and animals. Plankton play a significant role in ecosystems because many water organisms depend on them for food. The small animals that feed on plankton are the food for the bigger organisms (Suthers & Rissik 28). So, they are the base of the food chain and sustain the fish, amphibians, and reptiles in the lake. Because plankton anchor the food chains, ecologists need to understand their population dynamics to help in predicting the effects of variations. Also, it is necessary to study plankton because of their potential to cause lethal algal blooms for those that produce toxic chemicals.

In most ecosystems, the effects of drought are usually drastic and fatal. Drought lowers water levels in lakes while increasing the temperature and nutrient concentration. The fall in water quality leads to blooms in invasive algae and also increases the residence time of wastes. This paper reflects on a study conducted by Beaver et al. between 2007 and 2015. Lake Mead has three bases; Colorado River, Overton Arm, and the Las Vegas Bay and the scientists collected samples from all the sites (Beaver et al. 89). They used a multi-parameter submersible sonde unit to measure water quality, the Utermo hl sedimentation technique to measure zooplankton samples, and used Leica DMLB compound microscopes to observe phytoplankton.

Further, they used EPA method 544, followed by HPLC/MS to determine algal toxins and applied niche centroid analysis combined with quadratic regression models to measure niche centroids and temperature intervals. They observed that the temperatures at Lake Mead range between 11 to 310C through the year, and that Daphnia pulex complex planktons dominated in winter while Daphnia galeata mendotae dominated the lake in spring (Beaver et al. 91). They also noted no significant changes in phytoplankton populations and species composition inter-annually. The surface temperature also proved to be a major determinant of plankton species variations.

At Lake Mead, D. pulex is the most dominant zooplankton followed by Daphnia galeata mendotae, and their densities were highest in winter and spring. The phytoplankton included Microcystis species., Cyclotella species., cyanobacteria, and other phytoplankton and the peaked during spring and summer (temperatures between 18 to 300C) (Beaver et al. 92). Forage fish, sportfish like largemouth bass, and striped bass entirely depend on zooplankton for food. As a result, largemouth bass and striped bass peaked when there was high Daphnia biomass at the lake. Thus, it is convincing to deduce that the fish productivity at the lake is the result of the interaction of phytoplankton, zooplankton, and nutrient concentrations in the water.

Since these patterns were relatively consistent throughout the research years, it spurs curiosity to know the mechanisms deployed by the plankton to beat the climatic disturbances.

Invasive species are the other significant ecological challenges to plankton population in the lake. Dreissenid mussels eat small cladocerans and rotifers (small zooplankters) and compete with zooplanktons for food (Beaver et al. 89). The competition can shake up the trophic arrangements among zooplankton, phytoplankton, nutrients, and fish to cause reduced water turbidity and a higher water clarity; which may interfere ultimately with plankton population (Suthers & Rissik 41). Increase water clarity exposes large-bodied plankton such as D. pulex complex to predators, thus threatening their density. Similarly, young gizzard shad feed solely on zooplankton and can decimate the crustacean zooplankton in a lake when it infests. However, maturing and mature gizzard shad increase the water turbidity and reduce clarity. The effects can thus raise the phytoplankton population in the lake.

In 2015, a sudden increase in Microcystis aeruginosa released many harmful toxins into Lake Mead, which got detected for the first time. The toxicity spread uniformly across all zones of the lake. Typically, cyanobacteria densities rise when phosphorus levels are high. But at Lake Mead, Microcystis spp out-competed the other cyanobacteria under low phosphorus level and high nitrogen levels.

Microcystis species were highest at temperatures of from 15 to 30oC, and their optimum performance is when they reside at the upper layer of the water. In the 2015 bloom, the scientists observed a significant M. aeruginosa population deep down the water. The species bloom and toxicity also lead to higher temperatures of the lake waters. Gizzard shad, Dreissenid, and quagga mussels have proven to worsen toxic cyanobacteria bloom (Beaver et al. 89). A repeat in poisonous blooms in the lake could be harmful to the dominant plankton species, and the harm could cascade to higher trophic levels. Lastly, drought also encourages cyanobacteria proliferation by lengthening the water residence time and increasing surface temperature.

The ecological theory explains that environmental stresses in habitat may evoke responses on the residents. Still, the reactions may not be linear or measurable initially, until they reach some threshold (Suthers & Rissik 28). An example of a non-linear change is the 2017 toxicity bloom. Before then, surface temperature patterns had remained relatively constant year on year, and the same was true for plankton population dynamics. The Lake Mead ecosystem stability comes about as a result of its morphology (size and depth) and lower average temperatures when compared to other ecologies (Davies & Keith 57). However, in line with the ecological theory, the effects may continue to grow until the ecosystem is overwhelmed, and the impacts become more severe with more toxic blooms.

Lake Mead's ecology is a resilient one that shows little to no response to the myriad of environmental stressors that currently torment it. Abnormal weather conditions and reduced snowpack could have caused the 2015 toxicity bloom. For now, it is not yet predictable how continued drought and invasion by species could affect the future of Lake Mead.

Works Cited

Baker, John R. Limnological Aspects of Lake Mead, Nevada-Arizona. Denver, Colo: United States Department of the Interior, Bureau of Reclamation, Engineering and Research Center, Division of General Research, Applied Sciences Branch, 2012. Print

Beaver, John R. et al. "Long-Term Trends In Seasonal Plankton Dynamics In Lake Mead (Nevada-Arizona, USA) And Implications For Climate Change". Hydrobiologia, vol 822, no. 1, 2018, pp. 85-109. Springer Science And Business Media LLC, doi:10.1007/s10750-018-3638-4. Accessed 14 Dec 2019.

Davies, B R, and Keith F. Walker. The Ecology of River Systems. Dordrecht [The Netherlands: W. Junk, 1986. Print.

Suthers, Iain M, and David Rissik. Plankton: A Guide to Their Ecology and Monitoring for Water Quality. Collingwoo, Australia: CSIRO Publishings, 2009. Print.