Importance of habitat diversity to changes in benthic metabolism over land-use gradients: Evidence from three subtropical estuaries

Abstract

Seasonal rates of benthic gross primary production, net primary production and respiration were measured and whole-system carbon budgets constructed in 3 subtropical estuaries with different catchment land-use intensities to better understand how land-use changes influence benthic metabolism. Annual benthic net ecosystem metabolism (NEM) indicates that systems become more heterotrophic with increasing land-use intensity. This is due to a combination of an increase in the area of unvegetated habitats and the unvegetated habitats becoming more heterotrophic with increasing land-use intensity. Whole-system NEM is closely linked to benthic NEM, highlighting the important control of benthic metabolism on whole-system metabolism in shallow coastal systems. Carbon mass balances show whole-system net metabolism also shifted from net autotrophic to net heterotrophic, with a concomitant switch from CO₂ uptake to emission, with increasing land-use intensity. Our findings demonstrate that land-use changes shift whole estuary metabolism by altering both habitat distribution and within-habitat metabolism rates.