Hydromorphological restoration stimulates river ecosystem metabolism
Both ecosystem structure and functioning determine ecosystem status and are important for the provision of goods and services to society. However, there is a paucity of research that couples functional measures with assessments of ecosystem structure. In mid-sized and large rivers, effects of restor...
| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2017-04-01
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| Series: | Biogeosciences |
| Online Access: | http://www.biogeosciences.net/14/1989/2017/bg-14-1989-2017.pdf |
| Summary: | Both ecosystem structure and functioning determine ecosystem status and are
important for the provision of goods and services to society. However, there
is a paucity of research that couples functional measures with assessments of
ecosystem structure. In mid-sized and large rivers, effects of restoration on
key ecosystem processes, such as ecosystem metabolism, have rarely been
addressed and remain poorly understood. We compared three reaches of the
third-order, gravel-bed river Ruhr in Germany: two reaches restored with
moderate (R1) and substantial effort (R2) and one upstream degraded reach
(D). Hydromorphology, habitat composition, and hydrodynamics were assessed. We
estimated gross primary production (GPP) and ecosystem respiration (ER) using
the one-station open-channel diel dissolved oxygen change method over a
50-day period at the end of each reach. Moreover, we estimated metabolic
rates of the combined restored reaches (R1 + R2) using the two-station
open-channel method. Values for hydromorphological variables increased with
restoration intensity (D < R1 < R2). Restored reaches had lower
current velocity, higher longitudinal dispersion and larger transient storage
zones. However, fractions of median travel time due to transient storage were
highest in R1 and lowest in R2, with intermediate values in D. The share of
macrophyte cover of total wetted area was highest in R2 and lowest in R1,
with intermediate values in D. Station R2 had higher average GPP and ER than
R1 and D. The combined restored reaches R1 + R2 also exhibited higher GPP
and ER than the degraded upstream river (station D). Restoration increased
river autotrophy, as indicated by elevated GPP : ER, and net ecosystem production (NEP) of restored
reaches. Temporal patterns of ER closely mirrored those of GPP, pointing to
the importance of autochthonous production for ecosystem functioning. In
conclusion, high reach-scale restoration effort had considerable effects on
river hydrodynamics and ecosystem functioning, which were mainly related to
massive stands of macrophytes. High rates of metabolism and the occurrence of
dense macrophyte stands may increase the assimilation of dissolved nutrients
and the sedimentation of particulate nutrients, thereby positively affecting
water quality. |
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| ISSN: | 1726-4170 1726-4189 |