Organic pollution

Threats to Freshwater

Organic Pollution

  • Various sources of organic pollution include:

    • Domestic Waste: Mainly fecal matter from sewerage systems.

    • Industrial Effluents: Contributed by industries such as brewing, food processing, papermaking, and abattoirs.

    • Rainwater Drainage: Includes organic material such as:

      • 17 grams of dog feces per square meter each year.

      • Organic matter from rubbish tips and farmland (fertilizers, livestock farming, silage).

Nitrogen Pollution

  • Nitrogen from human activities is a significant contributor to water pollution.

  • Millions of metric tons of reactive nitrogen enter U.S. environments annually, leading to severe ecological impacts.

    • Source: Reactive Nitrogen in the United States—Report to the EPA Science Advisory Board.

Effects of Organic Pollution

Water Quality Changes

  • Turbidity and Sedimentation:

    • Affects light penetration and substratum conditions.

    • Causes algal blooms due to increased nutrients (NH4 – N, PO4 - P).

  • Microbial Activity: Supports the growth of microbial communities, indicated by:

    • Sphaerotilus, a filamentous bacteria that consumes oxygen.

    • Increased turbidity leading to reduced water quality.

Self-Purification

  • Processes involving natural filtration and decomposition mechanisms by microorganisms, which breakdown pollutants.

Alternative Stable States in Ecosystems

  • Clear vs. Turbid Water:

    • Eutrophic lakes can alternate between clear and turbid states.

    • Example: Lake Tåkern in Sweden.

  • Factors influencing stability:

    • Macrophytes favor clear states, while phytoplankton can lead to turbid conditions

    • Increased nutrient inputs can result in high biomass of phytoplankton.

  • A documented shift in 1995 linked to high precipitation and nutrient transport.

High Nutrient Conditions

  • Stratification: Refers to layers in lakes ranging from:

    • Epilimnion (warm, upper layer).

    • Metalimnion (middle layer).

    • Hypolimnion (cold, bottom layer).

  • Eutrophic conditions lead to high productivity, influencing gas concentrations.

Biochemical Oxygen Demand (B.O.D.)

  • Defined as the amount of dissolved oxygen required by aerobic organisms to decompose organic material.

    • High BOD indicates low oxygen saturation in water, leading to Dissolved Oxygen Deficit (DOD).

  • Key factors affecting B.O.D.:

    • Oxygen demand, dilution effects, and temperature variability.

Effects on Aquatic Organisms

  • Changes in oxygen levels and nutrient concentrations directly affect biodiversity:

    • Species Composition: From clean water fauna (e.g., Ephemeroptera, Plecoptera) to pollution-tolerant organisms (Tubificidae, Chironomus, Sphaerotilus).

Case Study: River Thames, U.K.

Historical Context

  • 19th Century: Severe pollution led to cholera epidemics and "The Big Stink" in 1858.

  • Developed sewage systems in 1844 and 1865 mitigated many issues.

Recent Rehabilitation

  • 1950s: One of the most polluted rivers, with low oxygen levels; extensive fish kills.

  • 1960s: Investment in sewerage treatment yielded significant improvements.

  • By 1976, all sewage was fully treated, leading to a resurgence in fish populations.

Current Issues and Challenges

  • Continuous investment in revitalization efforts post-1989.

  • Flooding has caused problems with sewage overflow in areas like Oxfordshire and Buckinghamshire, harming local ecosystems.

Eutrophication Case Study: Lake Washington

Historical Overview

  • 1933: Initially an oligotrophic lake later subjected to eutrophication due to rapid population growth (300 in 1865 to 1.2 million in 1965).

  • By the 1960s, the lake was referred to as “Lake Stinko” due to severe pollution.

Ecological Shifts

  • Notable decline in water clarity and biodiversity due to sewage influx, increasing dominance of cyanobacteria (Oscillatoria) over diatoms.

Positive Changes Implemented

  • Sewage Diversion: Initiated in 1963, completed by 1968, resulting in drastic reductions in phosphorus and improved ecological health.

  • Increased Daphnia populations contributing to clearer waters.

Water Treatment Options

Different Treatment Levels

  • Primary Treatment: Involves screening and settlement of solids.

  • Secondary Treatment: Utilizes biological organisms (bacteria, protists) to further breakdown waste.

  • Tertiary Treatment: Focuses on removing nitrogen and phosphorus to prevent further eutrophication through nitrification and phosphate removal methods.

Discussion Questions

  1. Examine the influence of oxygen concentration, particularly at greater depths, in aquatic ecosystems.

  2. Consider the reversibility of problems associated with eutrophication and the effectiveness of implemented solutions.