NON-POINT SOURCE POLLUTION
Pollution of all types is a threat to coastal areas throughout the world. Non-point source pollution cannot be traced to any one place or person (a point source), making it difficult to track and eliminate. Examples of non-point source pollution include nutrient contamination from agriculture; petroleum contamination from boats, refineries, and small leaks; and harmful chemicals that enter the water as runoff from highways, parking lots, and industrial sites through storm drains. In south Louisiana, non-point source pollution can be especially troublesome because we are downstream from many agricultural fields and industrial sites. In order to preserve our way of life, and preserve our natural environment, we must monitor water quality to prevent these pollutants from doing severe damage.
Most living organisms require oxygen to thrive. On land, the concentration of oxygen in the air seldom varies from 21% (21 parts of oxygen in every 100 parts of air). In water, however, the oxygen concentration varies in time and space. In fact, under some conditions, oxygen can become severely depleted. Hypoxia occurs when oxygen concentrations dip below 2 parts per million (ppm), and anoxia occurs when oxygen concentrations reach 0 ppm. Hypoxia is a common problem in our bayous and along the Louisiana coast. “The Dead Zone” is a large area on the Louisiana coast that regularly experiences hypoxia and cannot support marine life. Hypoxia can also occur in our bayous and bays, resulting in fish kills and other problems for wildlife. Hypoxia can result from many different processes. In the bayous, a combination of high temperatures, slow moving water, and (in some cases) pollution can cause hypoxia. In the Gulf of Mexico, hypoxia results from the decay of small plants (called algae or phytoplankton) that thrive in the nutrients transported by the Mississippi River. We monitor the concentration of oxygen and nutrients in the water to understand when hypoxia will occur and the effects it has on our environment.
CLick here for more information on hypoxia
OBSERVATIONAL VS. EXPERIMENTAL SCIENCE
Environmental monitoring is a type of observational science; we directly observe the conditions in the estuary without changing them. Scientists often conduct observational studies to describe the natural or man-made changes in a system over time. For example, if we are interested in how salinity in the estuary changes over time, we might monitor salinity at several locations on a monthly basis. Observational studies can also be used to test how the estuary behaves after a catastrophic event such as a hurricane or oil spill. However, these types of studies are unpredictable, because no one knows when or where the next hurricane will hit.
Observational science stands in contrast to experimental science, in which the scientist deliberately alters the conditions (e.g. temperature) to determine how the system reacts. For example, if we are interested in the growth of oysters in various parts of the marsh we might hypothesize that oysters grow better in low-salinity water. To test this hypothesis, we might grow oysters in several tanks filled with water of varying salinity. We must be careful to make sure that each oyster gets the same amount of food and that other variables (such as temperature) do not affect our experiment. In order for our experiment to be meaningful, we must compare our result to an undisturbed condition (a control treatment). For our oyster experiment, we could grow half our oysters in water from the site where they were collected. As you can imagine, it would be very difficult to conduct experiments on an entire estuary so experiments are usually conducted on a smaller scale than observational studies.
Data collection is common to both observational and experimental studies. The scientist (you) must record detailed measurements of interesting variables. To determine how the estuary changes in space and time, we must compare several measurements from different areas or time periods. During this field exercise you will be the scientist, collecting data to describe the conditions in the estuary.
A chief ingredient of scientific progress is the ability of other scientists to reproduce our methods and, hopefully, our results. Therefore, our methods must be clearly explained and our techniques thoroughly practiced. Here we have tried to provide an easy-to-follow set of instructions for collecting and processing water samples. By carefully following the written instructions, you can be sure that the data you collect is comparable to data collected previously and any data collected in the future.
The techniques you use to process your sample are just as important as carefully following instructions for achieving reproducibility. Therefore, as in all things, practice makes perfect. In the weeks leading up to your field trip, you should have been practicing using all of the gear. Each of you should have mastered using each piece of equipment before coming to LUMCON.
Many of our methods and techniques are designed specifically to avoid contamination of our samples and chemicals. For example, rinsing the sample containers thoroughly before collecting a sample is critical to avoid contaminating the sample with residues from previous samples. Just as important is the proper handling of chemicals to ensure that the reagents don’t become contaminated with sample water or with other reagents. This is important for two reasons. First, the methods we use are based on having pure chemical reagents. If our reagents are contaminated, our data are not useful and will not be reproducible by us or anyone else. Second, reagents are expensive and we need to preserve them for future samples. It is possible to ruin a whole bottle of reagent with a single drop of contaminant. Following these simple steps should eliminate the majority of contamination problems:
- Open only one reagent at a time and immediately recap the bottles with the same cap when done.
- Never touch the tip of a dropper bottle or pipette to the sample or the sample container.
- Rinse and dry sample containers thoroughly after use.
When scientists conduct a study, they must realize that the environment is constantly changing and that measurements made on a given day or at a certain location may not apply to every day or every location. That is why we need to collect samples on different days and in different locations. This is known as replication. Ideally, it is best to have several samples from a single site so that we can be sure that the data we report accounts for differences in conditions and errors caused by improper techniques. Proper replication is part of the reason that we have several groups collect samples at each sampling site.
Scientists rarely work alone and must be able to function as part of a team. The team is responsible for making sure that each piece of data is collected properly for each sample. It is possible for team members to specialize on a single task and be responsible for that one task (e.g. collecting a sample or recording results). However, it is usually better if all team members can perform all the tasks. That way no one gets bored, no one gets stuck with a yucky job all the time, and the team isn’t stuck if one member cannot participate for some reason. As part of the Bayouside Classroom, you should know how to complete each step of the sample collection and processing. For example, we usually work in teams of five people and can divide the tasks among the five team members as such:
- Task 1 (1 person): Sample collection and thermometer reading
- Task 2 (1 person): Salinity measurement
- Task 3 (2 people): Dissolved oxygen measurement
- Task 4 (1 person): Data recorder
Tasks should be rotated at each sampling station so that the work is divided equally.