MOSSA and WUDecadal-Scale Variations of Thalweg Morphology and Riffle–Pool Sequences in Response to Flow Regulation in the Lowermost Mississippi River

Chia-Yu Wu and Joann Mossa

Article first published online: 5 JUN 2019 Water

DOI: 10.3390/w11061175

ABSTRACT: The lowermost Mississippi River (LMR) is one of the largest deltaic systems in North America and one of the heavily human-manipulated fluvial river systems. Historic hydrographic surveys from the mid-1900s to the early 2010s were used to document the thalweg morphology adjustments, as well as the riffle–pool sequences. Extensive aggradation was observed during 1950s to 1960s, as the Atchafalaya River was enlarging before the completion of the Old River Control Structure (ORCS). Following the completion of the ORCS, reductions in sediment input to the LMR resulted in net degradation of the thalweg profile patterns since the mid-1960s except for the 1992–2004 period. Different flood events that supplied sediment might be the cause of upstream aggradation from 1963–1975 and net aggradation along the entire reach from 1992–2004. Furthermore, the change pattern of thalweg profiles appear to be controlled by backwater effects, as well as the Bonnet Carré spillway opening. Results from riffle–pool sequences reveal that the averaging Ws ratios (length to channel width) are 6–7, similar to numerous previous studies. Temporal variations of the same riffles and pools reveal that aggradation and degradation might be heavily controlled by similar factors to the thalweg variations (i.e., sediment supply, backwater effects). In sum, this study examines decadal-scale geomorphic responses in a low-lying large river system subject to different human interventions, as well as natural flood events. Future management strategies of this and similar river systems should consider recent riverbed changes in dredging, sediment management, and river engineering.

Read the full publication at Water

Murchison Elephants
Image courtesy of Dr. Sadie Ryan

GAINESVILLE, Florida – A new collection of research articles, jointly edited by Dr. Sadie Ryan and published by PLoS ONE examines the health and well being of captive elephant populations in North American zoos and preserves. This collection is sensitive in nature. While keeping large, socially complex, and long-lived animals, such as elephants, in captivity is controversial, many ‘wild’ populations of elephants in Africa and Asia are small and heavily managed, and the greater wild populations are in precipitous decline. Research such as this collection, on captive populations, can thus provide wildlife managers with well-quantified research to inform management strategies for in situ conservation.

Epidemiological Investigations of North American Zoo Elephant Welfare is published as a PLoS ONE Special Collection comprising nine research articles describing the results of studies across 68 participating zoos. The studies took an epidemiological approach, assessing how social, housing, and management factors influence elephant welfare, including abnormal behavior and reproductive health. This collection will play an important role in informing evidence based zoological management.

Working on this collection builds on Dr. Ryan’s long standing interest in small population management in endangered species, particularly elephants. Earlier in her career, Dr. Ryan worked at the Lincoln Park Zoo in Chicago, on demographic management of endangered species in captivity, and the impact of management practices on disease transmission and reproductive health. She has continued to work on issues of breeding and disease in captive populations, and continues to be interested in the implications from analyses of, and protection for, endangered species in captivity.

“This collection is specifically focused on the fundamentally important aspects of managing welfare for captive elephants, leveraging an unprecedented, massive collaboration among multiple zoological institutions,” said Ryan. “Without this kind of cooperation and effort to bring proper analyses of such vital, evidentiary information, we cannot properly protect the welfare of such an important set of species. While my bias is towards informing the protection and conservation of wild elephants, we are in a paradigm of small population biology across much of the wild population, and therefore this information is valuable both to collections and to the conservation of elephants, globally.”

The collection was edited jointly by Sadie Ryan (University of Florida) and Elissa Cameron (University of Canterbury).