# Mapping the Mangroves - MWL

## Introduction

Abiotic factors are the nonliving aspects of an ecosystem. Understanding how they shape an ecosystem and interact with biotic factors is a foundational stone of ecology/biology. Listed below are a number of abiotic factors that can be examined in a mangrove estuary along with associated background information. LaMotte makes a number of water test kits to facilitate this exploration.

• Students will measure and recognize abiotic factors in a mangrove ecosystem.
• Students will describe the role that abiotic factors play in mangrove ecosystems.

## Teaching Summary

The scope of this exploration can varied to fit the needs of the program. The exploration can be a single trip where the focus is introductory with regards to the tests, data collection, and interpretation of results. It can be expanded by looking at results collected over a 24 hour period, and their associated variations. And finally a data base can be established to examine seasonal change during a year, and from year to year. Below is a sample data collection sheet and associated questions.

Vocabulary: Nitrate, Nitrite, Phosphate, Salinity, Hydrometer, Osmosis, Aerobic, Anaerobic, Eutrophication, Thermoregulation

Abiotic factors and their associated tests:

• Dissolved Oxygen – Dissolved oxygen is measured with a tablet test, where color change indicates the amount of dissolved oxygen present in the water. High levels are better for most living organisms as oxygen in needed for cellular respiration, a key facet in metabolism.  Low levels put a strain on organism unless of course you are anaerobic. Factors that can affect oxygen levels include population numbers, open or closed estuary with regards to current, and pollution.
• Dissolved Nitrates, Nitrites, and Phosphates –  These are key compounds needed for cellular function like ATP, DNA, and cell membranes. These compounds are also tested with a tablet, and color results are used to indicate levels. In a healthy ecosystem, levels are usually moderate, with the compounds coming from the decomposition of dead organic matter and waste. High levels of these compounds usually result form sewage contamination, or heavy runoff after severe rains. High levels of these compounds can result in eutrophic conditions, which lead to algal blooms and extreme low dissolved oxygen levels.
• Biological Oxygen Demand – This test is an extension of the dissolved oxygen test. The pill dissolved in the test tube is stored for a 5 day period in a warm, dark area. Color results are then examined to determine amounts of oxygen still present. This test looks at microbial populations and their consumption of oxygen in cellular respiration and decomposition processes. A system with a high biological oxygen demand is typically represents degraded systems, with low biological diversity.
• Salinity – Salinity measures the amount of salt dissolved in water. A hydrometer is the instrument used for this process. A water sample is collected and the hygrometer is placed in the sample. A reading is taken from the instrument based on how high or low it is floating in the water sample. This reading is based on the samples density, which is determined by the amount of salt, dissolved in the sample. The reading is now compared to a chart that takes into account temperature to give a salinity reading. An understanding of osmosis and its relation to cellular function is important in recognizing how variable salinity can effect and organism. Ocean water typically has a salinity level of 35 parts per thousand. High salinity levels are found in areas with high rates of evaporation, and can lead to hypertonic scenarios in cells. Low salinity levels are typically found in areas with river systems entering, or in areas that have experienced heavy rainfall; low salinity levels lead to hypotonic scenarios in cells.
• Temperature – Temperature reading are collected with a thermometer. An excellent approach to temperature measurement is to establish an average temperature of a system and compare that to extremes found in deeper areas, shaded areas, and shallow areas. This concept can be taken a step further by collecting and comparing temperature data over a 24-hour period, or measuring temperatures over seasonal time frames. Roles of depth, latitude, seasonal change, etc… and their effects on the system will be examined. An understanding of thermoregulation in organisms will help facilitate discussions on the significance of temperature fluctuations in an ecosystem. Topics such as metabolism, migration, and behavioral change can be explored.
• ## Resources

LaMotte water testing kits and associated information.

## Assessment Questions

Questions

1. How might the days weather affect our salinity results?
2. Why are the nitrates and phosphates sometimes considered limiting factors in an ecosystem?
3. Identify different ways oxygen becomes dissolved in water, and ways in which it is consumed.