eutrophication: a reality that is threatening coastal areas

Eutrophica+on: a reality that is threatening

coastal areas

by Iván Loaiza Alamo

Course: Integrated Ecosystem Management and Ecological Engineering

Prof. Patrick Meire

Present status

Eutrophication -‐> an increase in the rate of supply of organic matter to an ecosystem, either by natural or human-‐driven, hence, the eutrophication is not a trophic state, is the process.

oligotrophic (<100)

mesotrophic (100-‐300)

eutrophic (301-‐500)

hyperthophic (>500)

in gC m-‐1y-‐1*

Past status

Source

: Nixon

, 199

5

Present status

Source

: WRI, 20

13

Eutrophic Hypoxia

Eutrophication

Useful to differentiate the NUTRIENTS FORM:

Dissolved organic nutrients -‐> high concentrations -‐> not bioavailable for organisms

Dissolved inorganic nutrients -‐> highly bioavailable -‐> converted in particulate organic matter (detritus, bacteria, phytoplankton, and marine snow).

Particulate inorganic nutrients -‐> suspended sediment

*Benthic and pelagic convertors -‐> dissolved to particulate, or organic to inorganic

Eutrophication

Coastal waters of the western Aegean Sea (E. Mediterranean) -‐> no Alexandrium minutum -‐> low support of N: P ratio requirements -‐> diatoms domination

Aegean Sea, Dodecanese Islands, Rhodes -‐ Greece

© Iván

Loa

iza

South Pacific Ocean, Piura Region, Sechura Bay – Peru

© Iván

Loa

iza

Coastal Ecosystems – Goods and services

Coral reefs Sea-‐grasses Salt marshes

Seafood, pharmaceutical industry, ornamental products, coastal protection, aesthetic and cultural. i.e. substances with anticancer, AIDS-‐inhibiting, antimicrobial, anti-‐inflammatory and anti-‐coagulating Ornamental species:

Direct and indirectly -‐> nutrient cycling, climate regulation, coastal protection, sediment stabilization and nursery and habitat services. 40 000 fish and 50 million of marine small invertebrates Traditional and local communities use as:

Coastal protection, nursery area for fish and breeding sites for birds. Ecosystem engineer with relevant functions in nutrient recycling and sediment accretion.

Nursery areas

Interconnection among ecosystems

Interconnected mosaic Sentinels

Source: Modified from the Global change and coastal hazard mitigation course, 2012

Eutrophication impacts

Ê  CORAL REEFS -‐> alteration of trophic structures, reduction of coral recruitment and diversity, replacement of corals by macroalgae and appearance of opportunist coral-‐eating crown-‐of-‐thorns starfish.

Ê  SEA-‐GRASSES -‐> a shift in community, from perennial seagrasses to phytoplankton, fast growing of opportunistic macroalgae, change of benthic and pelagic species composition and impairment of the system’s ability to store and cycle nutrients.

Ê  SALT MARSHES -‐> a decline in soil organic accumulation and consequential reduction of root and alteration in their long-‐term stability, related with the tidal range occupied, climate, sulfide accumulation, soil respiration, root physiology and soil quality.

Nutrient enrichment

CORAL REEFS -‐> reduction of calcification and higher concentrations of photopigments and diseases ≠ uptake by bacteria, phytoplankton and benthos -‐> organic matter in plankton and sediments. Particulate organic matter (POM) -‐> é food availability, tissue thickness, photosynthetic pigment concentration and calcification but threshold -‐> light attenuation.

SEA-‐GRASSES -‐> oxygen depletion, hypoxia in column water and anoxia in sediments -‐> lethal conditions for sea-‐grass and surrounding species communities. Shifts -‐> red macroalgae and unicellular diatoms to annual green and brown macroalgae and cyanobacteria *changing the pathway and turnover of carbon and nitrogen through benthic and pelagic food webs, potentially reducing ecosystem stability.

SALT MARSHES-‐> biomass belowground decreases and varies disproportionately with changes in aboveground biomass. Belowground live biomass -‐> no decreases at a threshold level (about 400 g m–2 at the end of the growing season). Nutrient-‐poor systems have the greatest amount of belowground biomass, which reduces with an increase in nutrient availability.

Light attenuation

Ê  CORAL REEFS-‐> slower calcification, thinner tissues and limited suitable areas for development -‐> affected by nutrient deposition and phytoplankton productivity. Toleration less than about 4% of surface irradiance, at 40 m in clear water or at 4 m in turbid water.

Ê  SEA-‐GRASSES-‐> high phytoplankton amounts, suspended solids and epiphytic algae on blades, and drift of macroalgal blooms + mixed + ammonia toxicity, low oxygen concentration, increased sediment sulfides and anoxia =

Sedimentation

Ê  Small sizes particles -‐> more damage than large particles -‐> rich organic matter and contaminants (i.e. pesticides) and high capacity in light absorbing.

Levels of ~12 mg cm−2 day−1 can kill newly settled corals with <48 h exposure if sediments are rich in organic contents, but such levels can be tolerated if the organic content is low.

Ê  The duration and amount of sediment exposure play an important role in the negative impacts and possible stress effects. High sedimentation rates (up to >100 mg dry weight cm−2) can kill exposed coral tissue within a few days, whereas lower rates reduce photosynthetic yields in corals within ~24 h

Sedimentation

Ê  Sedimentation exposure rates of 10 mg cm−2 day−1 are considered as threshold, causing harshly damaged in coral reefs.

Ê  High sedimentation rates and burial conditions -‐>50% of mortality of sea-‐grasses. Levels of 2-‐4 cm were enough to lead this level of mortality -‐> f (plant sizes)

Ê  Leaf size and the rhizome diameter are the best predictors of the capacity of sea-‐grasses to withstand burial. Sea-‐grasses were also vulnerable to sediment erosion.

Management approach and measurements: Sea-‐grass study cases

Restoration of degraded and impacted coastal ecosystems –> few successes

Ê  Dutch Wadden Sea -‐> Zostera marina in the early 1930s -‐ then many restoration attempts – high turbidity

Ê  Looking for the positive feedback -‐> water quality, hydrodynamics and substrate = equilibrium stage in sea-‐grass ecosystems

Ê  Small scales (<1ha) transplantations


Ê  Holmer et al. (2007) -‐> no variation of sediment nutrients among sea-‐grasses (Cymodocea rotundata and Thalassia hemprichii) and bare areas

Ê  HOWEVER -‐> releasing of oxygen (roots) -‐ éoxygen availability mineralization of organic matter nutrient availability

Ê  Sea-‐grass individuals of C. rotundata showed higher rate of photosynthesis and shoot density than T. hemprichii

Ê  The nutrient concentrations in the plant tissues were generally highest in the aboveground parts in both sea-‐grasses


Ê  High nutrient content 1.5–2.0% DW N and 0.18–0.20% DW P -‐> low organic content in sediments -‐> important role in uptake nutrients from the water column and nutrient cycling

Ê  SEA-‐GRASSES-‐> uptake of nutrients (roots & leaves) -‐> êeutrophic conditions – avoid ratios shift of N: P: SI, and concurrently food web changes

Ê  Phototropic species -‐> increasing of oxygen in sediment and along the column water -‐> enhancing the conditions for nutrient availability process -‐> reduction of hypoxia and anoxia levels

Management approach and measurements: Salt marsh study cases

Ê  Salt marshes are minimizing the eutrophication in transitional water, mainly through sedimentation processes such as nitrogen accumulation at high rate levels.

Ê  The Oldest Spartina Maritima salt marshes -‐> high annual belowground biomass and N productions / young marshes at aboveground level.

Ê  Ibañez et al., 2000 -‐> role in nutrients transformation and cycling (either functioning as sinks and/or sources)

*f (tidal marsh age, tidal energy, salinity, assimilatory nutrient uptake, N-‐fixation, oxygen release, nutrient production and losses)


Ê  Corroios salt marsh is an old marsh that is exposed to high sediment salinities and urban pollution -‐>N retained 2-‐to 3-‐fold higher than the other salt marshes -‐> reducing the aboveground production and investing in development a strong and resistant belowground material.

Ê  Pancas younger marsh -‐> higher percentage aboveground biomass than Corroio, salt marsh sediment -‐> 0.3% is inorganic N and more than 99% is organic N.


Ê  Caçador, 1999 cited by Sousa et al., 2008 mentioned that competition for nutrients is low in young marshes -‐> reduced amount of belowground material for living; this explains the higher aboveground biomass production in the youngest salt marshes.

Salt marshes have a crucial role on eutrophication reduction by taking up dissolved inorganic nitrogen for growth purposes, by enhancing N cycling through denitrification, and N retention through sedimentation processes -‐> f (biotic and abiotic characteristics and environmental parameters)

Conclusions

Ê  Eutrophication of coast areas has been increasing and widespread along the time, and apparently seems to be an irreversible pattern since 1980s.

Ê  Coral reefs, sea-‐grasses and salt marshes possess a broad type of ecosystem goods and services: coastal protection, sea and pharmaceutical products supply, ecosystem engineering (by their role in chemical, physical and biological processes), etc.

Ê  Mitigation and remediation of eutrophic ecosystems or ecosystems in eutrophication can be addressed by the development of a management approach using coastal ecosystems, as long as all the following factors: transplantation scale, water quality, turbidity, climate, currents, tide fluctuation, substrate, etc are considered.

eutrophication: a reality that is threatening coastal areas

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