Water Contamination Mapping Lab Purpose To teach basic principals of map analysis using actual Miami-Dade County spatial data and to explore the concept of environmental health, specifically in regard to water currents and the potential impact on water quality. Overview After a brief introduction to the Biscayne Bay Ecosystem, observed microbe distributions and water current maps are introduced. Data from an actual sewage main break in Biscayne Bay is presented and students are asked to hypothesize about microbes indicating sewage contamination may be found. A separate exercise presents a hypothetical case and has students measure water current speeds to predict the movement of pollutants based on the type of tidal flow. Time 1 two-hour class block. Key Concepts Flow of water in Biscayne Bay is primarily dependent on tidal movement and to a lesser extent wind induced motion, and outflows from the Miami River and other canals that discharge into the Bay. Water current data can be used to determine the areas that potentially could be impacted by a sewage spill. The distribution of microbes away from a source within Biscayne Bay can be partly explained through tidal action. There are other variables that impact the distribution such as tidal mixing and wind. Skills Interpreting spatial data Understanding how to use a legend and scale on a map Compiling information from different maps to explain trends Materials Overhead projector Transparencies Photo courtesy of DERM AMBIENT 76 Water Module
Facilitator Preparation These exercises are designed to complement the use of the sewage spill Scenario. If students are not familiar with the scenario, it would be helpful to review the basic facts, and perhaps show the video segment to the students to introduce the concept. Having read the Teacher s Guide to Water Quality will also prepare you to answer student questions during the exercise. Procedure Begin the exercise by showing the first two images (Biscayne Bay ecosystem and the sattelite map) on the overhead projector. On the satellite map, identify the area of the spill which is at the very top of the image. Have students describe what they see on the satellite map. The following pages, beginning with the Department of Health chart of Coliform Counts, are designed to be the subject of a class discussion. It may be useful to hand out a hard copy of this first sheet because the numbers in it are quite small and difficult to read on the overhead. Included at the end of the discussion section are some actual data sets from scientists who monitor tidal movement in Biscayne Bay. The section titled Vector Exercise is a take-home assignment which emphasizes estimation and basic math skills as applied to mapping. Further Investigation There are websites and other resources with geographic data which could be used in this mapping exercise. Students could seek data to supplement the maps included on the previous pages. Some possible resources: South Florida Water Management District http://www.sfwmd.gov/ Biscayne National Park U.S. Geological Survey http://www.nps.gov/bisc/ http://www.areaparks.com/biscayne/ http://www.usgs.gov/ Miami-Dade County Dept. of Environmental Management http://www.metro-dade.com/derm/ Student Assessment Give the following mapping components to each student team as a guide to their work: Interpret the maps to answer the questions Answer each question using the maps and data given Illustrate the questions on the maps provided Identify sewage impact areas If applicable, each group member should take the lead on at least 1 question AMBIENT 77 Water Module
Assign points for the following components of the Team Presentation: Were the students able to answer all the questions in both written and map form? Was the student able to answer questions about the facts and their conclusions, and defend their point of view? Were proper science terms used? Did the students report their sources? If applicable, was each group member actively involved in the mapping exercise? AMBIENT 78 Water Module
Biscayne Bay Ecosystem The ecosystem of Biscayne Bay includes the marginal freshwater and saltwater wetlands, intertidal communities, and marine communities. The health of each of these communities can be linked to their interaction with the hydrologic regime of South Florida. Major factors that may affect these communities are: The alteration and control of freshwater flow entering Biscayne Bay. Urbanization of Dade County, thereby increasing storm runoff and pollutants into Biscayne Bay. Natural and artificial changes to vegetation associated with fires and urbanization. Natural disasters, including hurricanes, and prolonged wet or dry seasons. The health of the Biscayne Bay ecosystem requires that a critical balance be maintained among the ecosystem communities. Significant changes in one will affect the others. Changes in the wetland communities (including vegetation) can alter surface water flow regimes and bird and fish behavior. Our ability to interpret historical changes, as well as to monitor future conditions, in the bay and surrounding area will allow us to improve or maintain the sensitive balance in freshwater quantity and quality necessary for the ecosystem components to continue a balanced existence. AMBIENT 79 Water Module
Satellite Image of Key Biscayne Hobie Beach RSMAS Key Biscayne Crandon Park Beach AMBIENT 80 Water Module
Here is the map of microbe levels at specific water sites around Miami-Dade County. The sample results are indicated as: T = Total Coliform Count F = Fecal Coliform Count E = Enterococci Count 1. Before looking at the chart at left, where would you expect to find high levels of fecal coliforms after the sewage spill? 2. What do the presence of fecal coliforms indicate? 3. According to the chart, which two sampling locations show the highest levels of total coliforms? 4. What do the minimum and maximum counts shown likely reflect? 5. What factors may account for the apparent concentrations of coliforms in areas distant from the spill? AMBIENT 81 Water Module
0 1000 2000 3000 Meters Water Speed 0.5 meters/sec. 0.25 meters/sec 0.15 meters/sec Miami Flood Tide Current Flow To Miami River Hobie Beach Bear Cut and Gov t Cut Key Biscayne Crandon Park Here is an approximation of the Biscayne Bay Flood Tide The incoming or rising tide is traditionally referred to as the flood tide because it floods the channel. The outgoing tide is referred to as the ebb tide. The strength of the ebb and flood tide velocities varies diurnally and over Spring Neap cycles in exactly the same way as tidal water levels vary (Spring Tides produce the fastest tidal currents). Biscayne Bay Safety Valve 6. Referring to the current scale, label each current arrow with speed. 7. Can you identify any areas in the bay where there are large tidal movements of water? Any particular direction? Fun Fact: Bay of Fundy-- has the greatest tidal range in the world with an occasional range of over 50 feet (15.2 meters) near the head of the bay!--the tidal range here is impressive. Caesar s Creek and Angelfish Creek Card Sound In Miami, tidal height differences are about 3-5 feet (.9-1.5 meters) normally. AMBIENT 82 Water Module Barnes Sound
0 1000 2000 3000 Meters Water Speed 0.5 meters/sec. 0.25 meters/sec To Miami River Hobie Beach Here is an approximation of the Biscayne Bay Ebb Tide 8. Referring to the current scale, label each current arrow with speed. 0.15 meters/sec Miami Ebb Tide Current Flow Bear Cut and Gov t Key Cut Biscayne Crandon Park 9. Are there any differences in the flow of currents besides direction? What influences the direction and magnitude of the currents? Biscayne Bay Safety Valve 10. What happens to contaminant substances in water after several tidal changes? Card Sound Caesar s Creek and Angelfish Creek Real World Applications: The data used in these maps are an approximation of the complex interactions of water, tides, topography, and other environmental factors. AMBIENT 83 Water Module Barnes Sound On the following pages, we illustrate actual models used by scientists to analyze water movement patterns in Biscayne Bay.
60000 Actual Flood Tide Model METERS 50000 40000 30000 20000 0.5 M/SEC These velocity fields in Biscayne Bay were obtained from results of a detailed hydrodynamic and salinity numerical model developed by Dr. John D. Wang with support from the National Oceanic and Atmospheric Administration (NOAA) Coastal Ocean Program award #NA37RJ0149 for research on the cumulative effects of stressors on the South Florida coastal environment. For more details, please visit http://cmea.rsmas.miami.edu and follow the links to Coastal Ocean Program, and Modeling of Physical Characteristics. 10000 2.0 1.5 AMBIENT 84 Water Module 0 1.0 24 48 72 10000 20000 30000 40000 METERS Half hours
60000 Actual Ebb Tide Model METERS 50000 40000 30000 20000 0.5 M/SEC These velocity fields in Biscayne Bay were obtained from results of a detailed hydrodynamic and salinity numerical model developed by Dr. John D. Wang with support from the National Oceanic and Atmospheric Administration (NOAA) Coastal Ocean Program award #NA37RJ0149 for research on the cumulative effects of stressors on the South Florida coastal environment. For more details, please visit http://cmea.rsmas.miami.edu and follow the links to Coastal Ocean Program, and Modeling of Physical Characteristics. 10000 2.0 1.5 AMBIENT 85 Water Module 0 1.0 24 48 72 10000 20000 30000 40000 METERS Half hours
Vector Exercise: 1. A sewage break has occurred at the contamination site (indicated by circle with B) shown on the Flood Tide Map. The break occurred early this morning during the beginning of Flood tide. a. Your task is to determine how long (in hours) it will take for the contaminated water to reach Hobie Beach and Crandon Park. b. Are there any other areas that may be impacted by the spill? Directions: Using the map scale, current speed and direction graphics, estimate current flow and speed using the following formula to predict a current path and time to arrival at each site (Hobie and Crandon), S = D/T (T=time D=distance S = speed) Hint: please note that the contaminant must travel around the land areas and pay attention to units (m/sec or m/hr) D = Hobie S = T = D = S = T = Crandon 2. Another sewage main break has occurred near the entrance to the Miami River (indicated by circle with C) shown on the Ebb Tide Map. The break occurred this afternoon during an Ebb tide. a. Your task is to determine how long (in hours) it will take for the contaminated water to reach Hobie Beach and Crandon Park. b. Are there any other areas that may be impacted by the spill? D = S = T = Hobie D = S = T = Crandon AMBIENT 86 Water Module
3. Considering that the tides cycle through flood and ebb every 12.4 hours, what effects would this sloshing of water have on a contaminant spill? AMBIENT 87 Water Module
Exercise Answer Key 1. Before looking at the chart at left, where would you expect to find high levels of fecal coliforms after the sewage spill? Before looking at the chart, one might hypothesize that the highest levels of fecal and total coliforms would be in the sampling locations nearest the spill, i.e. Virginia Beach and South Beach. 2. What do the presence of fecal coliforms indicate? Fecal coliforms are known as indicator microbes. They are typically measured to gauge the level of water contamination from human sources, such as sewage and runoff. 3. According to the chart, which two sampling locations show the highest levels of total coliforms? Haulover Beach and Hobie Beach 4. What do the minimum and maximum counts shown likely reflect? Given the sampling dates at the top of the chart, we can estimate that the minimum and maximum counts represent roughly the levels before and after the spill. 5. What factors may account for the apparent concentrations of coliforms in areas distant from the spill? Tidal mixing, and wind mixing to a lesser extent. Also, the movement of water around land masses, pooling in shallower areas with less flow. 6. Referring to the current scale, label each current arrow with speed. Large arrows are 0.5 m/sec; medium arrows are 0.25; small arrows are 0.15 m/sec 7. Can you identify any areas in the bay where there are large tidal movements of water? Any particular direction? Safety Valve. In general, tidal circulation of Biscayne Bay is in a southwest-northeast direction. On the flood tide, water goes into Biscayne Bay chiefly over the great flats, which include the "safety valve" between Biscayne Key and the Ragged Keys. 8. Referring to the current scale, label each current arrow with speed. Large arrows are 0.5 m/sec; medium arrows are 0.25; small arrows are 0.15 m/sec 9. Are there any differences in the flow of currents besides direction? What influences the direction and magnitude of the currents? The magnitude of the flow differs. In some places the current speed is faster than in others. The tidal cycle is largely governed by the gravitational pull AMBIENT 88 Water Module
between the earth and moon. Other factors, such as wind also affect the currents. Topography is also an important influence on water movement. In general, the upper layer of ocean water will move in the direction of the wind. The lower levels may or may not move in the direction of wind. 10. What happens to contaminant substances in water after several tidal changes? Contaminants will move back and forth with the tidal cycle. When the contaminant is carried with the general flow, this is called advective transport. As a contaminant undergoes advection, the contaminants will be mixed with surrounding uncontaminated water and in the process the contaminants will be dispersed and diluted. So the area of contamination will generally grow, and in the process the contaminants will become diluted. In some cases, contaminants can undergo reactions where they can decompose or produce new contaminants. In the case of microbes found in sewage, the microbes can die-off in which case the number of microbes will decrease. The microbes can also multiply, which will result in an increase in the number of microbes. Or, the number of microbes can stay the same. Please keep in mind that sewage contains many of the nutrients needed for microbes to grow. However, the salinity and temperature of the water may be such that the microbes will have a tendency to die-off. Vector Exercise Answer Key 1. A sewage break has occurred at the contamination site (indicated by circle with B) shown on the Flood Tide Map. The break occurred early this morning during the beginning of Flood tide. a. Your task is to determine how long (in hours) it will take for the contaminated water to reach Hobie Beach and Crandon Park. b. Are there any other areas that may be impacted by the spill? Directions: Using the map scale, current speed and direction graphics, estimate current flow and speed using the following formula to predict a current path and time to arrival at each site (Hobie and Crandon), S = D/T (T=time D=distance S = speed) Hint: please note that the contaminant must travel around the land areas and pay attention to units (m/sec or m/hr) D = 3000m S = 0.25 m/s T = 3.33 hrs Hobie 1. Convert formula to T = D/S then 3000m / 0.25 m/s = 12000 sec 2. Unit conversion 12000 sec / (I hr/3600 sec) = 3.33 hrs (Remember to round to significant digits) D = 3000m S =.15 m/s T = 5.56 hrs Crandon 1. Convert formula to T = D/S then 3000m / 0.15 m/s = 20000 sec 2. Unit conversion 20000 sec / (I hr/3600 sec) = 5.56 hrs (Remember to round to significant figures) b. Might impact Miami River and Downtown coast since water currents would reach areas in less than six hours when the tidal movements begins to change direction. AMBIENT 89 Water Module
2. Another sewage main break has occurred near the entrance to the Miami River (indicated by circle with C) shown on the Ebb Tide Map. The break occurred this afternoon during an Ebb tide. a. Your task is to determine how long (in hours) it will take for the contaminated water to reach Hobie Beach and Crandon Park. b. Are there any other areas that may be impacted by the spill? D = 2500m S = 0.25 m/s T = 2.78 hrs Hobie 1. Convert formula to T = D/S then 2500m / 0.25 m/s = 10000 sec 2. Unit conversion 10000 sec / (I hr/3600 sec) = 2.78 hrs (Remember to round to significant digits) D = 4500m S = 0.25 m/s T = 5.00 hrs Crandon 1. Convert formula to T = D/S then 4500m / 0.25 m/s = 18000 sec 2. Unit conversion 18000 sec / (I hr/3600 sec) = 5.00 hrs (Remember to round to significant digits) b. Might impact Hobie or Crandon especially since the tidal change will return the sewage to those areas thereby mixing the contaminants. 3. Considering that the tides cycle through flood and ebb every twelve hours, what effects would this sloshing of water have on a contaminant spill? First you need to consider the duration of the sewage spill. If the sewage spill is instantaneous (e.g. occurred over a very short period of time) then the contaminants would spread, mix with ocean water, and eventually be diluted to low concentrations. If the sewage spill lasted for a long period of time, then the contaminant concentrations would increase and the area affected would become larger and larger. At the outer fringes of the affected zones the contaminants would be diluted; however, in the inner zone where the sewage is spilling, the concentration would be very high. Note to Facilitator: Mixing refers to the intermingling of parcels of water as they are moved along the estuary under the influence of freshwater flows, tidal flows and secondary currents. Mixing not only involves an exchange of water mass, but also of any substance dissolved in it, such as salinity, dissolved pollutants, etc. Hence, mixing processes are of importance to the distribution of salinity and water quality levels throughout the estuarine water mass. AMBIENT 90 Water Module