Case Study Florida Everglades Mesocosm

This greenhouse-scale mesocosm is a 98 500 l butyl-lined, concrete block tank divided into seven connected sections of varying salinity (Figure 9). Each section contains water, algae, animals, sediments, and wetland-coastal plants representative of habitats along a transect from the full salinity Gulf of Mexico through the estuarine Ten-Thousand Islands and into the freshwater Florida Everglades (Figure 10).

As in the wild analog, the Gulf Shore and estuary are part of the same dynamic water mass. Here, the estuarine salinity gradient is created by pump-driven tidal inflow interacting through open weir constrictions and against downstream freshwater flow. Tank #1, the Gulf Shore, acts as a tidal reservoir for the estuary, thereby saving the need for a blank reservoir (Figure 11 ). The primary pump is an 800 lpm, Discflo™ unit that utilizes a rotating disk, rather than plankton-destructive impellers. The freshwater is derived from rain and from reverse osmosis extraction from the Gulf Shore (the equivalent of Gulf evaporation and resulting rainfall in the wild). All aquatic organisms, including adult invertebrates, can move from the estuary to the Gulf Shore. All organisms that can survive DiscfloTM pumping (including small fish) can return to the estuary via tidal inflow. The freshwater system, at times, flows directly into the uppermost estuary and technically all organisms can enter the estuary from freshwater.

The initial stocking of the mesocosm was completed in mid-1988, and small collections continued to be

Freshwater scrubber battery

Freshwater scrubber battery

Figure 9 Plan view of the Florida Everglades mesocosm and its critical engineering components.

nitrite plus nitrate in each of the community units (tanks); these were typically at levels of 5-8 mM (NO2 + NO3) through the middle of the estuary, and at 3-5 mM (NO2 + NO3), in the Gulf (#1) system. Levels average a few mM higher in winter than in summer. Nutrient flow-through is achieved by algal export, in the ATS banks. When levels drop below 1-2 mM in the Gulf (#1) system (typically in summer), the dried scrubber algae are redistributed to the system.

After 4 years of biotically closed operation, the Florida Everglades mesocosm was censused for organisms. The abundance of the principal higher plants, algae, invertebrates, and fish are shown in Figures 12-14. A total of 369 species (not including bacteria, fungi and the minor 'worm' phyla) was tallied. Excluding algae, protists, and small invertebrates, which could not be censused during introduction, it can be estimated that approximately 20-40% of the introduced species survived through the 4 years of biotic closure. In most cases these were the dominating species in the analog ecosystems. At the time of termination of the system as a carefully monitored mesocosm, only 15-30% of the originally introduced species were reproductively maintaining populations. However, in most cases, as Figures 12-14 show, these were the species that provided primary structure and metabolism in the analog ecosystem.

Everglades Ppt Background

Figure 10 Florida Everglades mesocosm approximately 4 years after construction showing salt marsh, black mangrove, and red mangrove communities (from front to background at left) and lower freshwater stream at right. At this point the greenhouse roof is providing a significant constraint to community succession by limiting vertical growth of mangrove and hammock trees.

Figure 10 Florida Everglades mesocosm approximately 4 years after construction showing salt marsh, black mangrove, and red mangrove communities (from front to background at left) and lower freshwater stream at right. At this point the greenhouse roof is providing a significant constraint to community succession by limiting vertical growth of mangrove and hammock trees.

injected through 1990. During this period, partial censuses for key organisms were undertaken, and, where required, additional stocking was carried out. From late 1990 to late 1994, the system was operated as a biotically closed system, with minor human interaction, functioning as an omnivorous predator.

Major physical/chemical parameters are shown in Table 3. Dissolved nitrogen was monitored as

System Freshwater Upper estuary Lower estuary Gulf Shore

Figure 11 Vertical/longitudinal section through Florida Everglades mesocosm showing water management system and tide levels.

System Freshwater Upper estuary Lower estuary Gulf Shore

Figure 11 Vertical/longitudinal section through Florida Everglades mesocosm showing water management system and tide levels.

Table 3 Physical/chemical parameters of the Florida Everglades mesocosm

Parameter

Tank #1

Tank #2

Tank #3

Tank #4

Tank #5

Tank #6

Tank #7

Temperature °C

Spring

23.4

23.2

22.5

22.6

22.0

21.3

23.2

Summer

25.7

25.5

25.4

25.7

25.6

25.1

25.1

Fall

22.2

22.3

21.8

22.0

21.7

21.3

22.1

Winter

21.0

20.9

19.9

19.6

19.0

18.4

21.9

Salinity, ppt

31.6

31.2

30.5

28.7

19.7

0.7

0.1

[NO2 + NO3] mM

Tap H2O as top upa

7.2

7.6

8.2

6.3

5.4

6.6

6.7

Milli RO as top upb

1.4

1.7

2.3

1.8

0.9

1.7

1.4

Tidal range cm/0.5 day

13-26

13-26

13-20

11-20

6-10

0-4

0

Hydroperiod cmyr"1

0

0

0

0

0

0

30.5

aNutrient levels in system as (NO2 + NO3) mM when 'Tap H2O as top up'.

b'Milli RO as top up' refers to mean system values when reverse osmosis water from Milli RO™ is used as evaporative replacement.

aNutrient levels in system as (NO2 + NO3) mM when 'Tap H2O as top up'.

b'Milli RO as top up' refers to mean system values when reverse osmosis water from Milli RO™ is used as evaporative replacement.

Case Study: Biosphere 2

Biosphere 2, located near Tucson, AZ, USA, is the largest greenhouse system ever built with nearly three acres (1.2 ha) of enclosed space. It is unique in surpassing any other greenhouse ecosystem in size, complexity, and duration of operation. The system was originally intended as a model of the Earth's biosphere (e.g., biosphere 1) with several tropical and subtropical ecosystems, an agricultural area, wastewater treatment wetlands, and a human habitat, along with a factory-sized machinery area for maintaining physical-chemical conditions. It was built to develop bioregenerative technology for future space travel, to educate the public about biosphere-scale issues and for basic ecological research. Atmospheric closure of gas cycles was part of the system design, which was tested with a prototype module of 11000ft3 (312m3) from 1988 to 1990.

A number of ecologists were consulted for the creation of the greenhouse's ecosystems which included plots of rainforest, desert, savanna, mangrove estuary, and ocean with coral reef. Thousands of species were added to the greenhouse intentionally and unintentionally (i.e., in ecosystem sub-blocks, as described above), from existing tropical systems as distant as Venezuela and from the local Arizona desert. After construction the ecosystems self-organized and

Benthic macroalgae of the Everglades mesocosm (dominant elements)

co E

CO 13

Gulf Coast

2 Red mangrove

Oyster Black Salt Oligohali n e Freshwater bays mangrove marsh marsh

System

# Species

Gulf Coast

2 Red mangrove

Oyster Black Salt Oligohali n e Freshwater bays mangrove marsh marsh

Lower estuary 14

Figure 12 Relative biomass of dominant benthic algae in Florida Everglades mesocosm.

many of the added species went extinct within the system as expected. Success, in terms of replication of the analog ecosystems in nature, has varied among the different model ecosystems, but most have developed and sustained a significant degree of ecological integrity.

Two experiments were conducted in Biosphere II during which humans were enclosed inside the system: the first for 2 years (1991-93) and the second for 6 months (1994). These experiments tested concepts of sustainabil-ity at a very basic level since the humans had to rely on the overall greenhouse system for life support function.

However, changes in the gas cycles within the greenhouse caused the human experiments to be modified and ultimately terminated. During the first human experiment oxygen concentration in the atmosphere decreased dramatically because high rates of soil respiration released more carbon dioxide than was taken up in photosynthesis; some of the carbon dioxide was absorbed as carbonates in the concrete of the greenhouse foundation. Oxygen had to be pumped into the system to maintain the humans so that the 2-year test could be completed. During the second human experiment, buildup of noxious concentrations of nitrous oxide in the atmosphere from microbial

Macroinvertebrates of the Everglades mesocosm (dominant elements)

Macroinvertebrates of the Everglades mesocosm (dominant elements)

System # Species

Predominant bottom type:

s. Hard, including mangrove Soft

2-4 Lower estuary

Salt Oligohaline marsh

Freshwater 11

Quit Coast

System # Species

Predominant bottom type:

s. Hard, including mangrove Soft

2-4 Lower estuary

Salt Oligohaline marsh

Freshwater 11

Figure 13 Relative invertebrate abundance in the Florida Everglades mesocosm.

Quit Coast

metabolism caused the experiment to be shut down ahead of the planned schedule.

At least two of the basic principles of ecosystem modeling discussed in the introduction were violated in this system. Incoming light was greatly reduced, due to the glass and significant support structure, resulting in insufficient photosynthesis and primary productive to balance respiration. This could have been offset by introducing a subset of highly efficient photosynthesis (such as provided by an ATS), using artificial lighting; indeed, some ATS systems were used, but only as a minor element of control on the ocean system. Monitored exchange with the external environment could also have been employed. Also, the concrete as an atmospheric reactant should have been sealed with a nonreactive material, such as glass or plastic.

Much controversy developed during these human experiments. Colombia University took over management of the system from 1996 to 2003. During this time period the research program changed from human enclosure experiments to work on global climate change.

Fishes of the Everglades mesocosm

Fishes of the Everglades mesocosm

System

2, 3, 4 Lower estuary

5, 6 Upper estuary

Gulf Coast

Freshwater

System

2, 3, 4 Lower estuary

5, 6 Upper estuary

# Fish In unit

94 +

118 +

17 +

11 +

102 +

Area of unit (m2)

44.7

34.8

7.6

7.6

37.4

# Individuals per m2

2.1

3.4

2.2

1.4

2.7

# Fish species

8

6

3

2

In Gulf:

y. Opsanus beta (gulf toadfish)

Haemulon macrostomum (spanish grunt) Lagodon rhomboides (pinfish) In Lower estuary:

Eucinostomus gula (silver jenny)

* Higher predators

In Gulf:

y. Opsanus beta (gulf toadfish)

Haemulon macrostomum (spanish grunt) Lagodon rhomboides (pinfish) In Lower estuary:

Eucinostomus gula (silver jenny)

Not reproducing

Possibly reproducing or reproduced in past Ratio of total individuals to reproductive adults

Figure 14 Distribution offish (% of total) in Florida Everglades mesocosm.

Gulf Coast

Freshwater

See also: Freshwater Lakes; Freshwater Marshes.

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