Mississippi River Floodplain Research Articles

Spatial variation in trophic ecology of small mammals in wetlands: support for hydrological drivers

AbstractFood webs composed of similar consumers can vary based on nutrient input, habitat structure, and other factors. For wetland‐associated species, fluctuating water levels can potentially affect habitat quality, which in turn can affect trophic diversity. Our objective was to determine spatiotemporal variation in the trophic structure of small mammals at two wetland complexes (floodplain and mineland) in southern Illinois. We live‐trapped small mammals during 2011–2013 at nine wetland patches on the Mississippi River floodplain and 14 patches at a reclaimed mineland. We collected hair samples from six species of small mammals (n = 428) at these wetland complexes. We analyzed C and N stable isotopes for three mammal taxa (Oryzomys palustris, Peromyscus spp., Microtus ochrogaster) to compare diet between species, sites, and times. Food sources (vegetation and invertebrates) were collected to form the isotopic baseline. We found no seasonal difference in diet composition, but isotopic values varied between sites and species. At the floodplain site, both δ15N and δ13C isotopic values for Oryzomys were more variable and completely enclosed that of Peromyscus. At the mining site, Peromyscus were at a lower trophic level (δ15N) and had a separate and less variable δ13C values from Oryzomys. Microtus was at a lower trophic position than the other two species at both sites. These results point to reduced niche overlap between Oryzomys and Peromyscus at the mining site, perhaps due to lower habitat quality and limited suitable resources. At the floodplain site, we conclude that more dynamic hydrology gave rise to higher biodiversity and more resources allowing small mammals to use similar food items.

Variation in metapopulation dynamics of a wetland mammal: The effect of hydrology

AbstractKey factors affecting metapopulation dynamics of animals include patch size, isolation, and patch quality. For wetland‐associated species, hydrology can affect patch availability, connectivity, and potentially habitat quality; and therefore drive metapopulation dynamics. Wetlands occurring on natural river floodplains typically have more dynamic hydrology than anthropogenic wetlands. Our overall objective was to assess the multiyear spatial and temporal variation in occupancy and turnover rates of a semi‐aquatic small mammal at two hydrologically distinct wetland complexes. We live‐trapped marsh rice rats (Oryzomys palustris) for 3 yr and >50 000 trap nights at nine wetland patches on the Mississippi River floodplain and 14 patches at a reclaimed surface mine in southern Illinois. We used dynamic occupancy modeling to estimate initial occupancy, detection, colonization, and extinction rates at each complex. Catch per unit effort (rice rats captured/1000 trap nights) was markedly higher at the floodplain site (28.1) than the mining site (8.1). We found no evidence that temperature, rainfall, or trapping effort affected detection probability. Probability of initial occupancy was similar between sites and positively related to patch size. Patch colonization probability at both sites was related negatively to total rainfall 3 weeks prior to trapping, and varied across years differently at each site. We found interacting effects of site and rainfall on extinction probability: extinction increased with total rainfall 3 months prior to trapping but markedly more at the floodplain site than at the mining site. These site‐specific patterns of colonization and extinction are consistent with the rice rat metapopulation in the floodplain exhibiting a habitat‐tracking dynamic (occupancy dynamics driven by fluctuating quality), whereas the mineland complex behaved more as a classic metapopulation (stochastic colonization & extinction). Our study supports previous work demonstrating metapopulation dynamics in wetland systems being driven by changes in patch quality (via hydrology) rather than solely area and isolation.

Missouri Ozark Plateau Headwaters Diversion engineering feat

T he Headwaters Diversion, a system of impounding basins, channels, and levees, carries the waters of the eastern Missouri Ozark Plateau hill streams eastward to the Mississippi River south of Cape Girardeau (figure 1). The system consists of three large basins, 78 km (50.3 mi) of channels, and 69 km (44.7 mi) of levees designed in 1910s by the Little River Drainage District (LRDD) to divert and temporarily store ordinary and flood waters running off 288,000 ha (720,000 ac) of the Francois Mountains and Ozark Plateau uplands (Burns 1919; Engineering Record 1914; LRDD 2012). Today, the Headwaters Diversion helps drain and protect 480,000 ha (1.2 million ac) of agricultural lands in southeast Missouri from internal seasonal flooding and Mississippi River backflow at flood stage (figure 1). It was constructed concurrently with an intricate network of 1,500 km (957 mi) of ditches, 375 km (242 mi) of levees, and water detention basins draining thousands of alluvial wetland hectares (acres) in the ancient Mississippi River floodplain running south from the diversion levee 144 km (90 mi) to the Arkansas border and is the focus of an upcoming article in the March/April 2016 issue of the Journal of Soil and Water Conservation (Olson et…

Effects of Flooding on Ion Exchange Rates in an Upper Mississippi River Floodplain Forest Impacted by Herbivory, Invasion, and Restoration

We examined effects of flooding on supply rates of 14 nutrients in floodplain areas invaded by Phalaris arundinacea (reed canarygrass), areas restored to young successional forests (browsed by white-tailed deer and unbrowsed), and remnant mature forests in the Upper Mississippi River floodplain. Plant Root Simulator ion-exchange probes were deployed for four separate 28-day periods. The first deployment occurred during flooded conditions, while the three subsequent deployments were conducted during progressively drier periods. Time after flooding corresponded with increases in NO3 −-N, K+ and Zn+2, decreases in H2PO4 −-P, Fe+3, Mn+2, and B(OH)4-B, a decrease followed by an increase in NH4 +-N, Ca+2, Mg+2 and Al+3, and an increase followed by a decrease for SO4 −2-S. Plant community type had weak to no effects on nutrient supply rates compared to the stronger effects of flooding duration. Our results suggest that seasonal dynamics in floodplain nutrient availability are similarly driven by flood pulses in different community types. However, reed canarygrass invasion has potential to increase availability of some nutrients, while restoration of forest cover may promote recovery of nutrient availability to that observed in reference mature forests.

Flood pulse effects on nitrification in a floodplain forest impacted by herbivory, invasion, and restoration

We tested the hypothesis that management actions that alter floodplain plant communities will modify the effects of flooding on gross nitrification, a key process regulating the flux of nitrate along river-floodplains. Soils were collected from mature forests, patches of Phalaris arundinacea, an exotic grass, and areas restored to early successional forest (unbrowsed and browsed) in the Upper Mississippi River floodplain. Samples were collected across an elevation gradient and along the descending limb of the hydrograph to test for effects of flooding. In all three forest types, soil properties were less favorable for nitrification as elevation increased, due to decreasing organic matter, porosity, total nitrogen, and temperature. In contrast, Phalaris maintained high soil organic matter and porosity as floodplain elevation increased. Corresponding with the differences in soil properties found in forested plots, the highest rates of potential gross nitrification were found in the lower elevation sites immediately following the spring flood (1–8 days post inundation). These high rates were later followed by a rapid decline in both NH4 +-N and nitrification with increasing time since inundation (>11 days post inundation). Nitrification rates were also highest following the flood in Phalaris sites, but rates did not depend on elevation, likely because of the lack of elevational differences in soil properties. Our results generally support the flood-pulse concept of river-floodplain connectivity, with the highest nitrification rates found in areas and during times immediately following inundation. Furthermore, restoration of forest cover in areas invaded by Phalaris appears likely to restore flood-pulse effects on abiotic soil properties and nitrification dynamics.

The role of water in the emergence of the pre‐Columbian Native American City Cahokia

Studies of the role of water in the emergence and maintenance of complex societies often span functional, political, and economic perspectives on water management with a particular focus on conservation and water storage. However, water is also symbolically important typifying urban environments like the Olmec site of San Lorenzo in Mexico, the Aztec city of Tenochtitlan, and Ancestral Puebloan sites in the North American Southwest. In fact, the symbolic and relational importance of water contributes to the location and emergence of some of the world's most prominent early cities and urban environments. In examining the role of water in the emergence of one of North America's largest pre‐Columbian cities, Cahokia (ca. AD 1050), it becomes apparent that early Native American people valued more than the functional properties of water, directly incorporating natural and man‐made water features into the city plan. Nestled into the naturally wet ridge and swale setting of the Mississippi River floodplain at the confluence of the Illinois, Missouri and Mississippi Rivers, water was a focal point of Cahokia's dynamic landscape impacting the location of earthen mounds, neighborhoods, causeways, and public plazas. Through an examination of the natural and built environments, I demonstrate the importance of water as symbolic and relational where Cahokians manipulated the natural environment to create a city that emerges out of a watery world. Understanding the relational and animate roles of water to the construction and maintenance of early urban environments can and does provide unique insight into ancient worldviews. WIREs Water 2015, 2:489–503. doi: 10.1002/wat2.1094This article is categorized under: Engineering Water > Planning Water Human Water > Water as Imagined and Represented

Sediment and nutrient trapping as a result of a temporary Mississippi River floodplain restoration: The Morganza Spillway during the 2011 Mississippi River Flood

The 2011 Mississippi River Flood resulted in the opening of the Morganza Spillway for the second time since its construction in 1954 releasing 7.6km3 of water through agricultural and forested lands in the Morganza Floodway and into the Atchafalaya River Basin. This volume, released over 54 days, represented 5.5% of the Mississippi River (M.R.) discharge and 14% of the total discharge through the Atchafalaya River Basin (A.R.B.) during the Spillway operation and 1.1% of the M.R. and 3.3% of the A.R.B. 2011 water year discharge. During the release, 1.03teragrams (Tg) of sediment was deposited on the Morganza Forebay and Floodway and 0.26Tg was eroded from behind the Spillway structure. The majority of deposition (86 %) occurred in the Forebay (upstream of the structure) and within 4km downstream of the Spillway structure with minor deposition on the rest of the Floodway. There was a net deposition of 26×10−4Tg of N and 5.36×10−4Tg of P, during the diversion, that was equivalent to 0.17% N and 0.33% P of the 2011 annual M.R. load. Median deposited sediment particle size at the start of the Forebay was 13μm and decreased to 2μm 15km downstream of the Spillway structure. Minimal accretion was found greater than 4km downstream of the structure suggesting the potential for greater sediment and nutrient trapping in the Floodway. However, because of the large areas involved, substantial sediment mass was deposited even at distances greater than 30km. Sediment and nutrient deposition on the Morganza Floodway was limited because suspended sediment was quickly deposited along the flowpath and not refreshed by incremental water exchanges between the Atchafalaya River (A.R.) and the Floodway. Sediment and nutrient trapping could have been greater and more evenly distributed if additional locations of hydraulic input from and outputs to the A.R. (connectivity) were added.

Cahokia’s emergence and decline coincided with shifts of flood frequency on the Mississippi River

Here we establish the timing of major flood events of the central Mississippi River over the last 1,800 y, using floodwater sediments deposited in two floodplain lakes. Shifts in the frequency of high-magnitude floods are mediated by moisture availability over midcontinental North America and correspond to the emergence and decline of Cahokia--a major late prehistoric settlement in the Mississippi River floodplain. The absence of large floods from A.D. 600 to A.D. 1200 facilitated agricultural intensification, population growth, and settlement expansion across the floodplain that are associated with the emergence of Cahokia as a regional center around A.D. 1050. The return of large floods after A.D. 1200, driven by waning midcontinental aridity, marks the onset of sociopolitical reorganization and depopulation that culminate in the abandonment of Cahokia and the surrounding region by A.D. 1350. Shifts in the frequency and magnitude of flooding may be an underappreciated but critical factor in the formation and dissolution of social complexity in early agricultural societies.

Fish Movements and Passage Through a Water Control Structure: River Stage and Floodplain Connectivity

The St. John's Bayou water control structure near New Madrid, MO, connects the main Mississippi River to two large backwater areas called the New Madrid Floodway and St. John's Bayou. While this area has been altered, the New Madrid Floodway and St. John's Bayou account for the only substantial portion of the historic Mississippi River floodplain that remains and provides the only critical connection between backwater/floodplain habitat and the river. Fish passage was evaluated during April–December 2010 using ultrasonic telemetry. Stationary receivers were placed strategically at five locations above and below the structure in St. John's Bayou, in the floodway and the outlet to the Mississippi River. A total of 100 individuals representing 14 species were tagged. Total number of detections during an 8-month period was 1 264 717. Fifteen individuals representing five species moved into the Mississippi and Ohio rivers; seven individuals returned to St. John's Bayou. Thirteen of the 14 species moved upstream through the structure. Of the 85 individuals that stayed in the bayou, 29 fish passed through the structure for a total of 92 passage events. The downstream : upstream passage was roughly 50:50. Passage was correlated with river rise, with frequency of passage being higher in spring, but passage occurred each month during the study. Copyright © 2015 John Wiley & Sons, Ltd.

The rise and fall of the Lower Mississippi: effects of hydrologic connection on floodplain backwaters

In the last 150 years, the Lower Mississippi River (LMR) floodplain was extensively reduced in area with conversion of once regularly inundated floodplain wetlands to dry land. Yet, between the present levees, there remain substantial remnants of the historical floodplain, including various types of permanent backwater habitats. We hypothesized that degree and timing of hydrologic connection with the river main channel drives variation in physical and chemical properties, and phytoplankton community dynamics, in backwaters. Over 23 months, measurements were made in several sites varying in connection with the main channel. At high stages, the channel and backwaters converged in having elevated turbidity, suspended solids and dissolved nutrient concentrations, reduced algal biomass and production, a seston C:N ratio indicating predominantly allochthonous organic matter sources, and a diatom-dominated community. When connection was reduced, backwaters declined in suspended sediments and nutrients, surged in production and biomass, had a seston C:N ratio reflecting autochthonous production, and switched to a community dominated by cryptomonad algae. With prolonged isolation, biomass-specific production became nitrogen limited and declined. By a conceptual model, we illustrate the seasonally variable role of permanent floodplain backwaters as major sources of algal organic matter, and potentially for nutrient sequestration, within the Lower Mississippi system.

Refugia and postglacial expansion ofAcroneuria frisoniStark & Brown (Plecoptera:Perlidae) in North America

We used mitochondrial cytochrome c oxidase subunit I to infer the demographic history of Acroneuria frisoni Stark & Brown, a widespread eastern North American stonefly. We sequenced 1510 base pairs from 348 individuals from 36 populations, obtained 160 haplotypes, and tested 3 major hypotheses: 1) Wisconsinan and Illinoian glaciations were vicariant events that separated western and eastern populations; 2) the Mississippi River floodplain was a postglacial barrier to dispersal of eastern and western populations; and 3) at least 2 genetically distinct glacial refugia existed, east and west of the Mississippi River. We also investigated other barriers, pathways to dispersal, and the relative importance of refugia to repopulation of northern areas. Species-distribution modeling of its Wisconsinan-glacial-age distribution placed A. frisoni at the far southern end of the current distribution and in other areas further south and west than it is currently known, and separated western and eastern populations. Eastern and western populations accounted for 70% of the variation in the data set (analysis of molecular variance), and the Mississippi River was a major barrier to gene flow (Bayesian phylogenetic analysis). We identified a western, Ozark Mountains clade (OZK), a Midwest clade (MDW) in central and western Tennessee, and an Appalachian Mountains clade (APP) in Tennessee and Pennsylvania. Members of the MDW clade recolonized once-glaciated and glacially influenced areas north of the Ohio River. Members of the APP clade appear to be confined to the Tennessee River valley and the Ridge and Valley province of the Appalachian Mountains. The Mississippi River floodplain prevented members of the OZK clade from recolonizing northern areas, except in southern Illinois. Comparison to other species with similar distributions points to refuge use and recolonization similar to that of a megalopteran. Our data will guide reintroduction of A. frisoni into areas of the Midwest from which it has been extirpated.

Pleistocene–Holocene transition in the central Mississippi River valley

Within the northern Mississippi embayment the ancestral Mississippi River flowed south through the Western Lowlands and the ancestral Ohio River flowed through the Eastern Lowlands for most of the Pleistocene. Previous investigators have mapped and dated the terraces of their respective braid belts. This current research investigates the three-dimensional aspect of the Quaternary alluvium north of Memphis, Tennessee, through the interpretation of 3374 geologic well logs that are 91.4m (300ft) deep. The braid belts are capped by a thin silt/clay horizon (Pleistocene loess) that overlies gravelly sand, which in turn overlies sandy gravel. The base of the Pleistocene alluvium beneath the Ash Hill (27.3–24.6ka), Melville Ridge (41.6–34.5ka), and Dudley (63.5–50.1ka) terraces of the Western Lowland slope southerly by 0.275m/km and all have an average basal elevation of 38m. Near Beedeville, Arkansas, the bases of these terraces descend 20m across a northeast-striking down-to-the-southeast fault that coincides with the western margin of the Cambrian Reelfoot rift.The maximum depth of flow (lowest elevation of base of alluvium) occurred in the Eastern Lowlands and appears to have been the downstream continuation of the ancestral Ohio River Cache valley course in southern Illinois. In traversing from west to east in the Eastern Lowlands, the Sikeston braid belt (19.7–17.8ka) has a basal elevation averaging 7m, the Kennett braid belt (16.1–14.4ka) averages 13m, the Morehouse (12ka) braid belt averages 24m, and the Holocene (≤10ka) Mississippi River floodplain has the highest average basal elevation at 37m. Along this easterly traverse the base of the Quaternary alluvium rises and the age of alluvium decreases. The eastward thinning of the floodplain alluvium in the Eastern Lowlands appears to be caused by decreasing Mississippi River discharge as it transitioned from the Wisconsinan glacial maximum to the Holocene.The base of the Holocene Mississippi River floodplain averages 23m higher in elevation than the Pleistocene floodplain bases in the Eastern Lowlands. This high suballuvial surface (platform) is bound by the tectonically uplifted Joiner ridge, Blytheville arch, Charleston uplift, and Bluff Line fault. The spatial relationship and similar histories of the platform and bounding structures suggest that Quaternary erosion and tectonics are related.

The Preglacial “Pliocene” Mississippi River

AbstractLate Neogene upland gravels of the Mississippi River Valley are interpreted to be terrace deposits of the Pliocene Mississippi and Tennessee Rivers. Previous investigators have identified large-wavelength paleo-meanders in these gravels in the state of Mississippi that indicate a paleo-discharge six to eight times greater than that of the modern Mississippi River, suggesting that the drainage basin of the preglacial Mississippi River may have extended into Canada. This study explores the extent of the preglacial Mississippi River by mapping upland gravels from 97 wells in Illinois; 80 gravel locations from geologic quadrangles in Illinois, northeastern Arkansas, and southeastern Missouri; and 557 gravel wells in eastern Arkansas, western Kentucky, and western Tennessee. The distribution of these gravels indicates that during the Pliocene, the Mississippi River flowed near its modern course. A longitudinal profile of a 50-m-thick Pliocene Mississippi River floodplain was constructed from northern I...

The impact of nitrogen contamination and river modification on a Mississippi River floodplain lake

Anthropogenic nitrogen contamination has increased in ecosystems around the world (frequently termed the “nitrogen cascade”). Coke production for steel manufacturing is often overlooked as a source of nitrogen to natural ecosystems. We examined sediment cores from a Horseshoe Lake, a floodplain lake located just East of St. Louis Missouri (USA) to test whether a coking plant effluent could be traced using stable isotopes of nitrogen and diatom microfossils. The distribution of δ15N values in surface sediment samples from the lake shows the highest values near the coking plant effluent. Stable isotopes of nitrogen from 4 sediment cores using a mixing model showed three sources of nitrogen since 1688 CE. The first source (active between 1688 and 1920 CE) had a calculated δ15N value ranging between −0.4 and 1.1‰ depending on the core. After 1920 a second source with a δ15N ranging between 10.6 and 15.4‰ became active. The change in these sources coincides with the construction of a coking plant on the lake shore. A third source with a value approximately 7.0‰ was present at all times and represents background. The diatom microfossil assemblages present from 1688 CE to the late 1800s are dominated by the planktonic species Aulacoseira granulata and periphytic and benthic genera Gomphonema, Cocconeis, and Lyrella. After the late 1800s the diatom assemblages are dominated by Staurosira species indicating a shift of species from high flow riverine environments to epipelic species from a lake environment. Diatom microfossils seem to track the reduction in flooding due to leveeing of the floodplain and the isolation of the lake from the river. Our results show how stable isotopes of nitrogen can be used to track nitrogen inputs from industrial sources. Diatom changes corresponded with changes in connectivity between the Mississippi River and its floodplain.

Cahokia: Ancient America’s Great City on the Mississippi by Timothy R. Pauketat (review)

Reviewed by: Cahokia: Ancient America’s Great City on the Mississippi by Timothy R. Pauketat William I. Woods Cahokia: Ancient America’s Great City on the Mississippi Timothy R. Pauketat. Penguin Books, New York. 2009. 194 pp. (ISBN 978-0-670-02090-4) One thousand years ago a city existed on the Mississippi River floodplain directly to the east of the present St. Louis. Called Cahokia after the historic aboriginal group who inhabited the site in the 18th century, this was the most extensive expression of population nucleation to have been produced prehistorically in America to the north of Mexico. The structure of the community was planned with clearly defined administrative/ceremonial zones, elite compounds, discrete residential neighborhoods, and even suburbs. An enormous central plaza and numerous immense [End Page 235] earthworks provide evidence of high organizational skills and great expenditures of labor. With a population peak of perhaps 15,000 or more individuals, Cahokia existed for approximately three centuries. Book reviews are difficult pieces to write. This is particularly true when you are well acquainted with the author and the subject. Consequently, I accepted this assignment with a sense of foreboding. Unfortunately, my instincts proved to be correct. The book has been described as “Mesmerizing” and indeed it is, but for the wrong reasons. We have all experienced phone calls around dinnertime from a stranger who asks “Do you love puppies?” and a series of other questions that elicit a similar affirmative answer. Once you are firmly in the routine the stranger asks you if you would like to have subscriptions to a number of magazines. By that time “yes” is the ingrained response and your dinner is getting cold, so you end up with a lifetime of paper that you never would have ordered on your own. Cahokia provides a similar scenario. The author of this volume, Timothy Pauketat, a professor at the University of Illinois, will start a story that everyone would agree with and spin it into the most implausible and merely fanciful or patently false conclusions. I found this unbelievable for a scholar who has spent his entire career working in the American Bottom region (this too is a problem) and surely should know better. When going through the specifics of the discussion in this book one has to keep in mind that no one ever saw and wrote about the contemporary Cahokia. It was abandoned hundreds of years before the first Europeans ventured into the Central Mississippi Valley. So, belief systems, methods of rule, and other lifeways that do not leave a tangible footprint are unknown and always will be. Pauketat clearly understands the problem of dealing with the prehistoric (i.e., societies for which written records do not exist). He states on page 6 “. . . archaeologists must take great care interpreting the clues left behind by ancient societies, or they may end up being fooled by misleading evidence of a great or noble history.” Somehow during the writing of this volume, he forgot his own admonition. Almost immediately the reader is beset with the unprovable and implausible. On page 2 it is suggested that Cahokians worshipped the Morning and Evening stars and that this idea came from Mesoamerica through priests’ vision quest travels to Mexico. This idea was part of the longstanding ravings by the retired Marquette University anthropology professor, Alice Kehoe, and is repeated over and over again. No one of any standing has ever accepted it and there is no evidence to prove any part of this notion. Mesoamerican belief systems are somewhat known due to the preservation of some written documents, fresco texts, engravings, and, of course, accounts by European observers and by the participants themselves. Fine, Mesoamericans had an elaborate cosmography; all cultures do. Mesoamericans also had pyramids, as did the Peruvians, Egyptians, and Chinese. They also had priests; any clear evidence for these specialists at Cahokia? No less an authority that James B. Griffin, the dean of Eastern North American archaeology, stated and provided in print on numerous occasions his view of Mesoamerican contact with the peoples of the Eastern United States. His conclusion was clear; there was absolutely no evidence for direct contact between Mesoamerica and Cahokia. The...

Changes in Spatiotemporal Land Use Patterns in Selected Hydrogeomorphic Areas of China and the USA

Differences exist in land use/cover pattern and its change between the P. R. China and the USA. In order to describe those differences, land use changes in representative regions were quantitatively analyzed and compared. Xiamen City, Changzhutan region and Liupan Mountains regions were selected to represent three different hydrogeomorphic areas of eastern, central, and western China, respectively, while the Goodwin Creek Experimental Watershed (GCEW) located in the north-central part of Mississippi in the bluff hills just east of the Mississippi River floodplain was chosen in the USA. By integrating historical Landsat TM imagery and geographical information system data, the spatiotemporal land use dynamics and conversion of land use in China and the USA between 1980 and 2010 were explored and compared. Results indicated an urban sprawl in eastern and central China, which encroached upon large amount of cropland, forest land and grassland. On the other hand, western China reclaimed cropland from grassland, forest land, which led to severe soil erosion between 1990 and 2000. Goodwin Creek Watershed of the USA converted 73.3% of the lost cropland into forest land, pasture and idle land, which accounted for about 90% in 2010. Further, counter-urbanization occurs in the GCEW due to favorable eco-environment for living. Compared with the land dynamic degree of the GCEW, eastern China is greater than it; western China is smaller than it while central China is almost equal to it. And the land use intensity index of GCEW is smaller than that of China all these years. Eastern China advocated ecological civilization in 2007 to meet the serious challenges of sustainable development. Western China started the Return of Land from Farming to Forestry and Grassland Project in 2000. The Changzhutan region in central China is served as the resource-saving and environment-friendly community in 2007, which will be favorable for the sustainable land utilization and protection of ecology. From the eco-environmental view, China might use the experience of USA for future reference.

Effects of flood frequency and duration on the allometry of community‐level stem size‐density distributions in a floodplain forest

Consistent with the self-thinning law of plant population ecology, Niklas et al. in 2003 proposed that stem size-density distributions (SDDs) of multispecies forest communities should change in very predictable ways as a function of the effects of past disturbances on average tree size. To date, empirical tests of this hypothesis have not been pursued in floodplain settings. SDDs were constructed using tree stem-size and density data from forest plots positioned along a flood frequency and duration gradient in the Upper Mississippi River floodplain. As flooding (both frequency and duration) increased, several small tree species were eliminated from forest plots and the persistent species increased in their size. Consistent with the predictions of Niklas et al., these changes corresponded with overall decreases in stem density, increases in average stem size, and reductions in both the Y-intercept and slope terms of the community-level SDDs. This study adds to a growing list of examples suggesting that theories related to forest community composition and biomass must account for both the broader effects of disturbances as well as the underlying biochemical processes that regulate plant growth. Further study is needed to fully address the role different disturbance frequencies play in determining plant density, diversity, average size, and associated size\frequency distributions.

Control of Reed Canarygrass Promotes Wetland Herb and Tree Seedling Establishment in an Upper Mississippi River Floodplain Forest

Phalaris arundinacea (reed canarygrass) is recognized as a problematic invader of North American marshes, decreasing biodiversity and persisting in the face of control efforts. Less is known about its ecology or management in forested wetlands, providing an opportunity to apply information about factors critical to an invader’s control in one wetland type to another. In a potted plant experiment and in the field, we documented strong competitive effects of reed canarygrass on the establishment and early growth of tree seedlings. In the field, we demonstrated the effectiveness of a novel restoration strategy, combining site scarification with late fall applications of pre-emergent herbicides. Treatments delayed reed canarygrass emergence the following spring, creating a window of opportunity for the early growth of native plants in the absence of competition from the grass. They also allowed for follow-up herbicide treatments during the growing season. We documented greater establishment of wetland herbs and tree seedlings in treated areas. Data from small exclosures suggest, however, that deer browsing can limit tree seedling height growth in floodplain restorations. Slower tree growth will delay canopy closure, potentially allowing reed canarygrass re-invasion. Thus, it may be necessary to protect tree seedlings from herbivory to assure forest regeneration.

Threshold effects of flood duration on the vegetation and soils of the Upper Mississippi River floodplain, USA

Most large rivers have experienced major changes in hydrology and land use over the past century, with concomitant effects on sedimentation, nutrient cycling and biodiversity. To restore and/or enhance these ecosystems, managers need to know where their efforts are most likely to succeed under current hydrologic regimes as well as under potential future hydrologic regimes. We therefore examined changes in forest vegetation and soils across a hydrologic gradient, expressed as flood duration during the growing season, for 320km of the Upper Mississippi River (UMR) floodplain.Soil texture was highly variable but trended toward finer grained sediments and >5% organic matter as flood duration increased from 0% to ∼40% of the growing season. Beyond 40%, soil texture was exclusively silt plus clay with >5% organic matter. The diversity of both the understory and overstory tree communities was also highly variable at sites that flooded for <40% of the growing season. However, understory diversity decreased as flood duration increased from 0% to ∼25% of the growing season and overstory diversity declined as flood duration increased from 0% to ∼40% of the growing season. Diversity estimates for both strata were uniformly low at sites that flooded for longer than ∼40% of the growing season. Beyond this point the proportional abundance of Acer saccharinum in the overstory exceeded 70%.Our results suggest that there is a threshold along the elevation gradient of this floodplain, corresponding with flood durations lasting ∼40% of the growing season. At lower elevation sites, flooding exerts primary control over forest soils and vegetation, restricting the former to silt plus clay with higher organic matter and the latter to a few highly flood tolerant species. The existence of such thresholds have implications for management of floodplain soil nutrient dynamics and plant diversity under existing hydrologic regimes, more natural hydrologic regimes and more extreme hydrologic regimes that may result from climate change.

PAST AND PREDICTED FUTURE CHANGES IN THE LAND COVER OF THE UPPER MISSISSIPPI RIVER FLOODPLAIN, USA

ABSTRACTThis study provides one historical and two alternative future contexts for evaluating land cover modifications within the Upper Mississippi River (UMR) floodplain. Given previously documented changes in land use, river engineering, restoration efforts and hydro‐climatic changes within the UMR basin and floodplain, we wanted to know which of these changes are the most important determinants of current and projected future floodplain land cover. We used Geographic Information System data covering approximately 37% of the UMR floodplain (3232 km2) for ca 1890 (pre‐lock and dam) and three contemporary periods (1975, 1989 and 2000) across which river restoration actions have increased and hydro‐climatic changes have occurred. We further developed two 50‐year future scenarios from the spatially dependent land cover transitions that occurred from 1975 to 1989 (scenario A) and from 1989 to 2000 (scenario B) using Markov models.Land cover composition of the UMR did not change significantly from 1975 to 2000, indicating that current land cover continues to reflect historical modifications that support agricultural production and commercial navigation despite some floodplain restoration efforts and variation in river discharge. Projected future land cover composition based on scenario A was not significantly different from the land cover for 1975, 1989 or 2000 but was different from the land cover of scenario B, which was also different from all other periods. Scenario B forecasts transition of some forest and marsh habitat to open water by the year 2050 for some portions of the northern river and projects that some agricultural lands will transition to open water in the southern portion of the river. Future floodplain management and restoration planning efforts in the UMR should consider the potential consequences of continued shifts in hydro‐climatic conditions that may occur as a result of climate change and the potential effects on floodplain land cover. Published 2011. This article is a U.S. Government work and is in the public domain in the USA.