Efforts to restore urban rivers require an understanding of human-influenced changes in channel substrates. This study uses three naturally-occurring oxbows in a 3.5 km reach of Swan Creek, flowing through the City of...Efforts to restore urban rivers require an understanding of human-influenced changes in channel substrates. This study uses three naturally-occurring oxbows in a 3.5 km reach of Swan Creek, flowing through the City of Toledo, Ohio (USA) to reconstruct historical changes in channel substrate. Human impacts in the watershed were: 1) land clearance for agriculture (peaking in 1900-1920) and for suburban housing tracts (peaking in 1945-1970), followed by 2) the post-1940 creation of more efficient urban run-off systems from streets, parking lots, housing developments, and shopping centers. Historical aerial photographs and maps from 1935, 1940, 1950, 1963, 1974, and 1994 were georeferenced using ground control points, input to ArcGIS, and have root mean square error (RMSE) ranging from 0.19 - 0.77 m (average RMSE = 0.47 ± 0.20 m) when compared to the 2006 digital ortho quarter-quadrangle (DOQQ) image used as the basis for comparison. Results showed that channel sinuosity continually increased from 1.88 (1935) to 1.99 (2006). Two oxbows probably formed in 1913, and the third formed in 1940. Sediment cores and trenches were used to recognize historical channel substrates. Age control was provided by <sup>14</sup>C geochronology and labels on food packaging materials found in flood layers. Grain-size analysis of channel substrates shows a historical coarsening-upward trend: the largest clast size interval (f<sub>5</sub>) changes from +0.78f in pre-1935 channels, to -1.15f in pre-1940 channels, to -1.69f in the 2006 channel. These results indicate recent urban runoff created fluvial pavements and increasing channel mobility as the stream removes legacy sediment from intrabasinal sediment storage.展开更多
Background Since the late 1990s,bigheaded carps(largely silver carp[Hypophthalmichthys molitrix]but also bighead carp[H.nobilis])have established throughout the lower Mississippi River basin.Using previously studied o...Background Since the late 1990s,bigheaded carps(largely silver carp[Hypophthalmichthys molitrix]but also bighead carp[H.nobilis])have established throughout the lower Mississippi River basin.Using previously studied oxbow lakes in the lower White River basin,Arkansas,we compared current(2017,“post-carp”establishment)fish assemblages to historical(2002,“pre-carp”establishment)fish assemblages.Fish assemblages were comprehensively assessed using multiple gears,including boat electrofishing,mini-fyke nets,and experimental small-mesh gill nets.Results T-tests suggested that fish assemblage indices of richness,diversity,evenness,and dominance were often greater(P<0.05)during the post-carp period as reflected by boat electrofishing and experimental gill nets.However,all indices were generally similar(P>0.05)between the pre-carp and post-carp period with fish assemblages depicted using mini-fyke nets.Nonmetric multidimensional scaling analyses indicated that fish assemblages differed structurally between pre-carp and post-carp periods.Assemblage differences were linked to both small and large abundance changes for more than 20 species.Abundances of gizzard shad(Dorosoma cepedianum),emerald shiner(Notropis atherinoides),pugnose minnow(Opsopoeodus emiliae),crappies(Pomoxis spp.),bluegill(Lepomis macrochirus),orangespotted sunfish(L.humilis),and yellow bass(Morone mississippiensis)declined between the pre-carp and postcarp periods.Conversely,abundances of weed shiner(N.texanus),pallid shiner(Hybopsis amnis),longear sunfish(L.megalotis),buffalofishes(Ictiobus spp.),and gars(Lepisosteus spp.)generally increased during the same period.Conclusions Although not possible to conclude assemblage shifts were entirely related to bigheaded carps due to the absence of an appropriate reference system where carps did not establish,the wide establishment of these carps is one of the most pervasive changes to have occurred in the lower White River ecosystem during the past two decades.Thus,it is probable to conclude that post-carp establishment observations from this study were at least,in part,attributable to bigheaded carp establishment.Impacts of further range expansions by bigheaded carps in the White River and other lower Mississippi River sub-basins are unclear,though this study suggests probable effects on native fish assemblages,underscoring the need for further research and monitoring.展开更多
文摘Efforts to restore urban rivers require an understanding of human-influenced changes in channel substrates. This study uses three naturally-occurring oxbows in a 3.5 km reach of Swan Creek, flowing through the City of Toledo, Ohio (USA) to reconstruct historical changes in channel substrate. Human impacts in the watershed were: 1) land clearance for agriculture (peaking in 1900-1920) and for suburban housing tracts (peaking in 1945-1970), followed by 2) the post-1940 creation of more efficient urban run-off systems from streets, parking lots, housing developments, and shopping centers. Historical aerial photographs and maps from 1935, 1940, 1950, 1963, 1974, and 1994 were georeferenced using ground control points, input to ArcGIS, and have root mean square error (RMSE) ranging from 0.19 - 0.77 m (average RMSE = 0.47 ± 0.20 m) when compared to the 2006 digital ortho quarter-quadrangle (DOQQ) image used as the basis for comparison. Results showed that channel sinuosity continually increased from 1.88 (1935) to 1.99 (2006). Two oxbows probably formed in 1913, and the third formed in 1940. Sediment cores and trenches were used to recognize historical channel substrates. Age control was provided by <sup>14</sup>C geochronology and labels on food packaging materials found in flood layers. Grain-size analysis of channel substrates shows a historical coarsening-upward trend: the largest clast size interval (f<sub>5</sub>) changes from +0.78f in pre-1935 channels, to -1.15f in pre-1940 channels, to -1.69f in the 2006 channel. These results indicate recent urban runoff created fluvial pavements and increasing channel mobility as the stream removes legacy sediment from intrabasinal sediment storage.
基金U.S.Fish and Wildlife Service—Gulf States Marine Fisheries Commission through the Gulf&Atlantic Regional Panel on Aquatic Invasive Speciesthe U.S.Fish and Wildlife Service—Lower Mississippi River Conservation CommitteeAdditional financial support and facilities were provided by the Aquaculture/Fisheries Center at the University of Arkansas at Pine Bluff(UAPB)
文摘Background Since the late 1990s,bigheaded carps(largely silver carp[Hypophthalmichthys molitrix]but also bighead carp[H.nobilis])have established throughout the lower Mississippi River basin.Using previously studied oxbow lakes in the lower White River basin,Arkansas,we compared current(2017,“post-carp”establishment)fish assemblages to historical(2002,“pre-carp”establishment)fish assemblages.Fish assemblages were comprehensively assessed using multiple gears,including boat electrofishing,mini-fyke nets,and experimental small-mesh gill nets.Results T-tests suggested that fish assemblage indices of richness,diversity,evenness,and dominance were often greater(P<0.05)during the post-carp period as reflected by boat electrofishing and experimental gill nets.However,all indices were generally similar(P>0.05)between the pre-carp and post-carp period with fish assemblages depicted using mini-fyke nets.Nonmetric multidimensional scaling analyses indicated that fish assemblages differed structurally between pre-carp and post-carp periods.Assemblage differences were linked to both small and large abundance changes for more than 20 species.Abundances of gizzard shad(Dorosoma cepedianum),emerald shiner(Notropis atherinoides),pugnose minnow(Opsopoeodus emiliae),crappies(Pomoxis spp.),bluegill(Lepomis macrochirus),orangespotted sunfish(L.humilis),and yellow bass(Morone mississippiensis)declined between the pre-carp and postcarp periods.Conversely,abundances of weed shiner(N.texanus),pallid shiner(Hybopsis amnis),longear sunfish(L.megalotis),buffalofishes(Ictiobus spp.),and gars(Lepisosteus spp.)generally increased during the same period.Conclusions Although not possible to conclude assemblage shifts were entirely related to bigheaded carps due to the absence of an appropriate reference system where carps did not establish,the wide establishment of these carps is one of the most pervasive changes to have occurred in the lower White River ecosystem during the past two decades.Thus,it is probable to conclude that post-carp establishment observations from this study were at least,in part,attributable to bigheaded carp establishment.Impacts of further range expansions by bigheaded carps in the White River and other lower Mississippi River sub-basins are unclear,though this study suggests probable effects on native fish assemblages,underscoring the need for further research and monitoring.
