River Metabolism along a Latitudinal Gradient across Japan and in a global scale

Abstract

Since temperature is a key factor affecting photosynthetic and respiration rates, the rates of gross primary production (GPP) and ecosystem respiration (ER) are expected to be lower for rivers at higher latitudes, while the net ecosystem production (NEP) rate likely decrease in rivers at lower latitude due to higher sensitivity of ER to temperature compared with GPP. To examine these possibilities, we estimated the ecosystem metabolism of 30 rivers located from 43.03°N to 32.38°N in Japan during summer using a Bayesian model with hourly changes in dissolved oxygen concentrations. In addition, we examined latitudinal trends of GPP, ER and NEP in a global scale by compiling and analyzing river metabolic data estimated in previous studies. Our analysis showed that both GPP and ER tended to increase with latitude, although these rates were positively related to water temperature in Japanese rivers. Global dataset of GPP and ER also showed increasing trend towards higher latitude. In addition, contrary to our initial expectations, NEP decreased with latitude and most rivers were net heterotrophic at both regional (Japanese rivers) and global scales. These results imply that the latitudinal temperature effect on river metabolism is masked by other factors not examined in this study, such as land use in the watershed, which play pivotal roles in explaining the latitudinal variation of river metabolism.

Latitudinal variation in freshwater mussel potential maximum length in Eastern North America

“…Their size and growth rates depend on food availability and temperature; as these environmental variables change, so should the mussels’ growth characteristics. Mussels primarily feed on phytoplankton and bacteria, whose abundance (correlated with ecosystem respiration) increases with nutrient availability, temperature, and latitude (Dodds et al., 2019; Gurung et al., 2019). Nutrient availability describes the available building blocks for mussel's food and is often increased by human‐dominated (agricultural) land use, which leads to higher stream productivity in human‐dominated streams (Finlay, 2011).…”

The effects of temperature and light on ecosystem metabolism in a Japanese stream

“…In Japan, several studies have used the open system, diel oxygen method to estimate GPP and ER for an artificial stream channel (Kayaba 2005), including those of 23 stream and river reaches in central Japan (Iwata et al 2007) and 27 rivers across Japan (Gurung et al 2019); however, the GPP and ER values obtained from these studies have been estimated for a short period of time (a few days) over a limited season (June and August). Moreover, these studies of Japanese streams (Kayaba 2005, Iwata et al 2007, Gurung et al 2019 did not evaluate the relationships between ecosystem metabolism and envi-ronmental factors, such as water temperature and light intensity. Clarifying the dependence of ecosystem metabolism on light and temperature in Japanese streams could be valuable for predicting the responses of stream ecosystem functioning to environmental change.…”