Impacts of Human Activities on Aquatic Ecosystems

DegradationExploitation

EnhancementResource Protection

Impacts of Human Activities on Aquatic Ecosystems

Exploitation

Urban and agricultural water supplies

Harvesting food and natural products

Energy and mineral supplies

Degradation

Waste-water discharge

Eutrophication

Accidental releases

Ocean dumping and disposal

Airborne contaminants

Water Regulation

Pathogens and marine toxins

Biomass removal

Impacts of Human Activities on Aquatic Ecosystems

Enhancement

Reservoirs

Lake fertilization

Lake restoration

Resource Protection

Monitoring change

National regulations, international agencies and global agreements

Aquaculture

Artificial reefs

Freshwater Ecosystems

• Invasive Species (e.g., zebra mussel, lamprey)

• Pollution • Habitat Modification

– Channelization– Dams– Draining wetlands– Changes in terrestrial landscape

Channelization• Channelization – the

dredging and straightening of stream channels

• Why?– Divert water for irrigation– Drain fields for agriculture– Increase “usable” land– Prevent flooding

Kissimmee River, FL1961

Present

Problems with Channelization

– Altered flow regimes• Many species not adapted

to different flows– Loss of habitat

• Within the stream– Dredging removes snags,

habitat complexity• Total stream area• Floodplains

low- and no-flow in remnant channels & encroaching exotics led to low O2 & fish kills

Dams and stream modifications

• Long history of modifying rivers– Egypt had irrigation ditches by 3200

B.C. and dams by 2760 B.C.

• Dams built per year steadily increased from around 1800 to a peak in the 1970’s.

Dams and stream modifications

• 75,000 dams over 2m tall, plus 2.5 million smaller dams in the U.S. alone

Effects of Dams

• Benefits:– Water supplies– Navigation– Hydropower– Flood Control

• Decreased frequency, but increased severity

Physical Effects of Dams• Alterations of flow

– Prevents movement of sediment, nutrients downstream

– Slower flows upstream• leads to settling of sediment• reservoirs can fill by as much as 80% in 12 years

– More unpredictable flows downstream– Disturbs normal flood-pulse in spring

• Interchange of nutrients between river and floodplains

Biological Effects of Dams• Interrupts fish migration (e.g., salmon)

– Fish ladders can help– Still can have 10-20% fish loss during

outmigration

Biological Effects of Dams• Loss of important spawning/foraging

habitat in floodplain– Net economic loss - river fisheries more

productive than reservoir fisheries

– Changes in plant communities, reduced species richness below dams

Human Health Effects of Dams

Aswan Dam, Egypt –completed in 1970

Schistosomiasis (Bilharzia )

Parasite passes from humans to snails to humans

Irrigation from lake provided more habitat for snails

Wetlands• Wetlands – Transitional habitats between aquatic

and terrestrial environments, where water table is at or near the surface– Includes marshes, swamps, bogs, estuaries,

temporary ponds, etc.

• Estimated loss of 53% of total wetlands in U.S.– 9.2 million acres lost between 1950’s-1970’s– 2.6 million acres lost between 1970’2-1980’s– current loss of 124,000 acres per year

Wetland Loss

• Wetlands provide important ecosystem services– 1. Mitigate flooding

– 2. Retention of sediments, nutrients, pollutants• Natural sewage treatment plants

– 3. Wildlife habitat • 20% of threatened and endangered

species associated with wetlands• Important habitat for waterfowl

Wetlands: restoration• No-net loss of wetlands rule ~1989

– Developers must recreate wetlands they destroy in construction• Are new wetlands really the same?

Human Impacts on Marine Systems

• Many threats to words oceans

• We will focus on:

– Overfishing

– Aquaculture

– Coral reefs

Oceanic Fisheries• Worldwide, 25% of animal protein

• 70% of world’s marine fisheries are overexploited or in danger of becoming overexploited

Oceanic Fisheries• Number of fish caught rose steadily until 1990’s,

but per capita number caught decreased– Human population growing faster than increase in catch

• Leads to increased demand and overfishing– many species commercially extinct - no longer

economically profitable to harvest

Sustainable harvest• Ideal strategy: harvest population to

maximize growth rate– determines how quickly fish can be

removed, while still maintaining healthy stock

– too little or too much harvest, population grows slowly

– keep population at half carrying capacity

Most fisheries harvest too much

Why overfish?• Economics - Tragedy of the Commons

– Each group tries to maximize individual returns at expense of common resource

• Quota problems– Often a fixed number, not percentage– Harvesting constant number of

decreasing population leads to severe impacts

Why overfish?• Technological

“Improvements”– e.g., Bottom trawlers vs.

hook and line• problem of bycatch -

killing non-target animals

Overfishing Example: Bluefin Tuna• Large, wide ranging, fast animal

– Grows to 1500 lbs.– Swims up to 50 mph– Can migrate across oceans

• One of most valuable and over-exploited fish– Single fish sold for $172,000 in Tokyo

fish market auction - sashimi– Adult population declined 90% since

1975• 250,000 to about 22,000

Overfishing: Bluefin Tuna

Is Aquaculture the answer?• Aquaculture - breeding and raising of fish

and shellfish for food• Rapidly increasing industry• Provides 1/4 world’s marine fisheries

Aquaculture• Arguments for aquaculture

– 1. Not depleting natural fish stocks– 2. No bycatch– 3. More efficient

• Problems– 1. Still depleting natural fish populations

• Feeds often include fishmeal from wild populations• 2-5 kg wild fish to produce 1 kg raised fish

– especially problematic for carnivores fish (e.g. salmon)

Aquaculture• Problems (cont.)

– 2. Fish wastes• aquatic pollution, disease spread

– 3. Genetic diversity• raised fish escape and breed with wild fish• reduces genetic diversity• can cause migration problems

– 4. Can still be bycatch• if wild fish used to stock pens/ponds• Milkfish in Philippines

– 85% of fry collected NOT milkfish

Aquaculture• Problems (cont.)

– 5. Habitat destruction - loss of mangroves, coastal wetlands habitats• provide nursery habitat for fish/shellfish• protect coast from storms• help control floods• trap sediments• filter and clean water of excess nutrients

• Solutions?– Reduce fishmeal in feeds, raise more herbivorous fish

(e.g. Tilapia), regulations on building new facilities

Coral Reefs• One of most diverse and productive

ecosystems• Support at least 1/3 marine fish• Protect coasts from storms• Uptake carbon

Threats to Coral Reefs• Most threatened marine habitat• Major problems include:

– 1. Trawling and dynamite fishing - breaks up reefs

Threats to Coral Reefs2. “Bleaching” - death/loss of algae

• Triggered by stress– elevated temperatures– pollutants

• Frequency and severity have increased in the last decade

Threats to Coral Reefs• Problems (cont.)

– 3. Runoff• sediments, pollutants

– 4. Aquarium industry• collect best coral, animals

– 5. Global warming• rising sea levels - corals need shallow water• rising temperatures

– corals exist in very narrow temperature range

• Solutions - creating marine reserves, control development, regulate collecting

Why should I care about coral reefs?

• Tourism– Countries w/reefs get about 50% of their GNP from

reef activities

• Beach protection from waves

• Medical uses– AZT, 50% of cancer research, bone-grafting

• Biodiversity– 1% of ocean floor houses 25% of marine species

Points to know

1) What is channelization? Why is it done and what problems can it cause?

2) What can be the problems with dams and flood control? How do they affect sediment & water flows, fish migration, and floodplains?

3) What is a wetland and how much has been lost in the U.S.? What ecosystem services do they provide?

4) Why is oceanic fishing important (2 reasons)? Name 3 reasons for overfishing. What does the bluefin tuna example tell us about the effects politics & conflict of interests on fishing policies?

5) What are the pros and cons of aquaculture?6) Why should you care about the destruction of coral reefs?

EVALUATION FORM

• Instructor/Course Survey Form Faculty Course Evaluations are the primary method for evaluating teaching performance and allows students to make significant contribution to the evaluation of an instructor's performance. The Evaluation is one method of exposing good and bad qualities of courses and instructors. Please take a few minutes to fill out and submit the Evaluation. Your comments are anonymous. Course: ENVS 415 Title of the Course: Aquatic Ecology Instructor: Dr. Subodh Sharma Semester: Fourth Year First Semester

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