Discriminating anthropogenic climate change from natural climate oscillation signals in dissolved organic matter export from headwater catchments.
Abstract
Headwater catchments are potential sentinels for climate change because their hydrology and biogeochemistry respond to changing environmental conditions at scales appropriate to changes in both weather and climate. Scientific investigations focusing on changes in climate-driven environmental change would benefit by understanding changes in the export pattern of dissolved organic matter, "DOM signatures", from headwater catchments. However, climatic change has complex influences on headwater catchment dynamics, and to determine the effects of climate change, we must be able to discriminate between anthropogenic climate warming (non-stationary linear trends) and natural climate oscillation (stationary oscillating cycles) signals within catchment DOM yields from catchments. We present an analytical framework based on wavelet theory for analyzing non-stationary and stationary signals in yearly time series of DOM yields. This analytical framework was used to test the following hypotheses: That yearly DOM yields in headwater catchments contain both non-stationary and stationary climate signals; That non-stationary signals are greater than stationary ones; And that the effects of these signals are greater in catchments with lower rates of change in water loading and lower water storage capacity (i.e., are more directly linked to atmospheric conditions). We applied this framework on the yearly time series of DOM yield from catchments in the Turkey Lakes Watershed in Ontario, Canada and show that DOM signals appear "decoupled". In all catchments, dissolved organic carbon (DOC) showed no non-stationary (declining trends) despite showing declining yearly water yields, but catchments with relatively lower water loading (lower elevation on windward side of mountain) showed stronger and larger DOC export than those with higher water loading (high elevation on same side of mountain). In contrast, catchments showed both significant declining trends and oscillating cycles in yearly time series of dissolved organic nitrogen (DON) and total dissolved phosphorus (TDP) yields. Furthermore, those catchments with lower water loading rates show larger rates of decline and larger amplitudes of oscillating cycles, and among the low water loading catchments, those catchments with larger water storage capacity exported more DON and TDP during the oscillating cycles. Wavelet coherence analysis revealed correlations between global climate oscillation indices and DOM export, with DOC stationary signals most correlated to the longer oscillation AMO, while DON and TDP stationary signals most correlated to shorter oscillations of ENSO or NAO. Generally, catchments with lower water loading had strong non-stationary and stationary signals, suggesting that these catchments act as good sentinels to detect climatic signals. Collectively these small catchments contribute a large proportion of water to larger catchments and therefore they may have considerable influence on the productivity and biodiversity of surface waters in larger catchments.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFM.B13I..02C
- Keywords:
-
- 0400 BIOGEOSCIENCES;
- 0429 BIOGEOSCIENCES / Climate dynamics;
- 0470 BIOGEOSCIENCES / Nutrients and nutrient cycling;
- 1804 HYDROLOGY / Catchment