The mangrove mesocosm of Biosphere 2: Design, establishment and preliminary results

Abstract

Biosphere 2 is a specially constructed, 1.25 ha, greenhouse in southern Arizona, USA that is atmospherically and materially isolated from Biosphere 1, the Earth. Housed inside are living recreations of five natural ecosystems and an agricultural zone. Techniques were developed for the transplantation, maintenance and establishment of a diverse neotropical estuarine ecosystem model (referred to here as the mangrove mesocosm). Technical systems were designed for the simulation and control of environmental conditions including rain (0–3 1 s −1), wind (0–11 km h −1), air (5–50°C) and water temperature (15–35°C), water circulation (0–20 1 s −1), salinity (0–45 ppt), relative humidity (10–85% RH) and nutrient removal (up to 20 g-N d −1). In or near the mangrove mesocosm permanent sensors monitored and recorded at 15-min intervals the following ranges: light above (5–35.5 E m −2 d −1 and 1600 μE m −2 s −1 maximum) and below (0.5–5 E m −2 d − 1) the mangrove canopy; air (18–42°C) and water (16–27°C) temperature; salinity (25–35 ppt); relative humidity (50–80% RH); pH (7.6–8.1); dissolved oxygen (3.8–5.5 mg 1 −1); and several biogenic gasses including oxygen (20.5-14.5 ppm), CO 2 (500–4500 ppm), methane (0–50 ppm), nitrous oxide (0–80 ppm) and hydrogen sulfide (0–0.1 ppm). From November 1990 to December 1993, mangrove height increased approximately 250%v for each of the three mangrove species: Rhizophora triangle (red mangrove), Avicennia germinans (black mangrove) and Laguncularia racemosa (white mangrove). The spreading mangrove average canopy area increased by 374, 533 and 647% for the red, black and white mangroves, respectively. The mangroves organized into a closed canopy, maturing forest under the unique set of conditions found inside of Biosphere 2. Concurrent litterfall and decomposition monitoring experiments were initiated in October 1992 in the mesocosm and at Florida-based analog research sites. Reproductive litterfall and total litter-fall approximated the seasonal patterns found at the field sites. Both total and reproductive litterfall production in the mesocosm exceeded field levels (except for white mangrove) but fall within reported rates for Southwest Florida. Total litterfall and total reproductive litterfall for the mesocosm red (1281.1 g m −2 yr −1; 178.3 g m −2 yr −1) and black (635.2 g m −2 y −1; 64.6 g m −2 yr −1) mangroves exceed the Florida field site red (948.3 g m −2 yr −1; 89.2 g m −2 yr −1) and black (461.7 g m −2 yr −1; 16.3 g m −2 yr −1) mangrove rates. The field white mangrove total litterfall and total reproductive litterfall (766.3 g m −2 yr −1; 215.9 g m −2 yr −1) rates were greater than that produced by the mesocosm white mangroves (654.8 g m −2 yr −1; 67.6 g m −2 yr −1). In addition to being a useful system for mangrove ecology, the mesocosm is on display for public education and awareness of the need to conserve wetland areas.