Mangrove wetland productivity and carbon stocks in an arid zone of the Gulf of California (La Paz Bay, Mexico)

Mangroves provide multiple ecosystem services (ESs), including fish and wildlife habitat, protection from coastal erosion and flooding impacts, food resources, water quality, carbon sequestration and storage. However, most of the mangrove wetlands structural and functional information useful to evaluate the quality, quantity and monetary value of its ESs has been obtained from studies at tropical latitudes usually dominated by large deltas and extensive coastal lagoon and estuaries. Thus, there is a major data gap for mangrove wetlands located in arid and semi-arid regions due to their limited land cover and location at the boundary of transitional climate gradients. Here we analyze the spatial distribution of mangrove wetlands carbon stocks and net primary productivity (i.e., litterfall and root productivity) in La Paz Bay, an arid coastal region in the Gulf of California, Mexico, where mangrove wetlands are spatially distributed in conspicuously extensive patches. We used this information to qualitatively rank ESs. Three peri-urban mangrove wetland sites (Balandra, Enfermeria, and Zacatecas) were characterized by different degrees of anthropogenic impact. Aboveground biomass (interval: 13.6 to 31.6 Mg C ha(-1)) was in the lower range when compared globally. The average C storage in mangrove soils (at 45 cm depth) in La Paz Bay is 175 Mg C ha(-1), which is higher than the values reported for other arid zones (>= 1 m soil depth: 43-156 Mg C ha(-1)). Belowground root biomass and productivity values (roots range: 0.22-0.31 Mg C ha(-1); fine roots NPP: 0.06-0.09 Mg C ha(-1) yr(-1)) were in the lower range. We found distinct differences in aboveground C storage values among sites where mangrove species formed monospecific stands across the landscape within each site. Areas dominated by the species Rhizophora mangle reflected the highest soil C density values (208.9 +/- 144.6 Mg C ha(-1)), followed by Laguncularia racemosa (181.4 +/- 118.2 Mg C ha(-1)) and Avicennia germinans (155.5 +/- 72.1 Mg C ha(-1)). We identified ESs provided by each of the sites, including both cultural (i.e., ecotourism; especially in Balandra), and provisioning (fisheries) services. Our study is a first step in the quantitative assessment of functional and structural properties as ESs of arid mangrove wetlands in La Paz Bay that could be readily translated into robust economic estimates for this arid coastal region.