Nutrient release from moose bioturbation in aquatic ecosystems

Abstract

While the ecological importance of bioturbation is well recognized and the prevalence of aquatic foraging by terrestrial ungulates is increasingly appreciated, research linking how terrestrial ungulates function as disturbance mechanisms via bioturbation in freshwater systems is lacking. The purpose of this study was to quantify potential nutrient pulses released from benthic sediments into the water column when moose Alces alces feed on aquatic plants. We also determined if we could experimentally mimic the benthic disturbance and the expected nutrient pulse created when moose feed aquatically. When moose foraged aquatically, significant releases of both total and dissolved phosphorus (P) and nitrogen (N) resulted in the waters that were disturbed in foraging areas compared to adjacent undisturbed waters. Nutrient concentrations for total P and N ranged from 42.5 × and 2.7 × greater in disturbed than undisturbed, respectively. Dissolved P and N were 26.8 × and 1.5 × greater, respectively, in disturbed versus undisturbed waters. Our experimental mimic created increases of total and dissolved P and N that were equivalent to pulses created by moose. This indicates that it is possible to experimentally test by proxy the potential impact of moose bioturbation on other ecosystem processes. This study is the first quantification of moose foraging as a consumer mechanism that influences the release of limiting nutrients in aquatic systems, thereby emphasizing the potential cascading importance for nutrient uptake and productivity of plants and microbes.

Environmental Predictability as a Cause and Consequence of Animal Movement

“…For example, migrations lead to periodic environmental dynamics (i.e., contingent on time) that are beneficial to many resident species [13]: the yearly Serengeti migration leads to a periodic influx of nutrients in the Mara river [14], as do fish spawning migrations in many riverine ecosystems [78]. Some ungulates, when feeding on aquatic plants, release pulses of nutrients by bioturbation [79]. If these individuals use space periodically, we can expect these pulses to be themselves predictable (highly contingent on time), but to our knowledge this has not yet been investigated.…”

Carbon dynamics of river corridors and the effects of human alterations

“…Within aquatic habitats, moose can stimulate nutrient fluxes through bioturbation of sediments, with potential effects on OC cycling (Bump et al. ). The net effect on OC dynamics of altering aquatic and riparian animal assemblages thus depends on the species affected and the intensity of the alteration, but such alterations have received relatively little attention in terms of their potential net effects on OC dynamics within river corridors.…”

“…Studies in boreal forests indicate that high densities of moose can cause declines in CO 2 uptake by vegetation and storage in plants and soil, as well as influencing humidity, soil temperature and moisture, and fire regime (Schmitz et al 2003). Within aquatic habitats, moose can stimulate nutrient fluxes through bioturbation of sediments, with potential effects on OC cycling (Bump et al 2016). The net effect on OC dynamics of altering aquatic and riparian animal assemblages thus depends on the species affected and the intensity of the alteration, but such alterations have received relatively little attention in terms of their potential net effects on OC dynamics within river corridors.…”

Cross‐ecosystem effects of a large terrestrial herbivore on stream ecosystem functioning

“…For example, in Yellowstone National Park, USA, loss of riparian vegetation by over‐abundant ungulate browsing caused river channel widening and erosion (Beschta and Ripple ). Many large ungulate species play important roles in connecting terrestrial and aquatic ecosystems via their foraging behavior (Moss , Bakker et al ) yet few studies have investigated the impacts of large ungulates on aquatic ecosystems (Bakker et al , but see Beschta and Ripple , Bump et al , , Vanschoenwinkel et al , Subalusky et al , ).…”

“…Theory shows that subsidies, like the ones described above, are a potential mechanism driving the strength of trophic cascades (Huxel and McCann , Leroux and Loreau ), primary and secondary productivity (Polis and Hurd ), and nutrient cycling within and across ecosystems (Leroux and Loreau , Gounand et al ). Large terrestrial ungulates are common in many biomes but the few studies that have examined their impacts on aquatic ecosystems have focused on lakes (Bump et al ) or large rivers (Subalusky et al ).…”