Recent history of sediment deposition in marl- and sand-based marshes of Belize, Central America

There are two contrasting types of wetlands in Belize: marl- and sand-based marshes. We measured accumulation rates of sediment in six cores from marl- and sand-based marshes of northern Belize and compared biogeochemical characteristics to assess recent wetland history (1850 to present). Sediment depth increments were analysed for bulk density, LOI, nutrients (C, N, P, S, Ca, Mg, K and Na) and snail shell density and species diversity. Cores were dated using ²¹⁰Pb and a constant rate of supply model. Unsupported ²¹⁰Pb inventories of the cores ranged from 6.16 to 8.92 pCi cm⁻². Marl-based marshes showed the maximum peak of ²¹⁰Pb activity from 4 to 10 cm below the sediment surface. ²¹⁰Pb peaks corresponded with the bottom of a marl layer containing chlorophyll a and we suggest that this relationship reflects the high growth and decomposition rates of cyanobacterial mat. Inorganic carbon, Ca, Mg, K, Na, S and Pb contents and accumulation rates were much greater in the marl-based marshes than in the sand-based marshes. Average dry mass accumulation rates in the six marshes ranged from 113 to 572 g m⁻² year⁻¹ over the past 100 years. Average linear sedimentation rates during the last 100 years in the two types were not significantly different (0.93 and 1.08 mm year⁻¹, respectively). Increased sediment accumulation by human activities such as soil washout from adjacent roads was recorded in a sand-based marsh near roads. Sediment cores in the marl-based marshes display changes of marsh vegetation, apparently caused by water level changes. The vegetation change occurred at the end of the 1800s and the beginning of 1900s and is represented by a band of dark peat in otherwise marl-dominated sediments. Overall, the sediment cores show that conditions were relatively undisturbed by human activities in the recent past.     

The ecology of urban landscapes: modeling housing starts as a density-dependent colonization process

Data on permits for new housing starts are a key source of information on recent changes in the urban landscape of central Arizona, USA. Drawing primarily on the conceptual parallels between the process of urban expansion and the spatial spread of non-human species, we outline a nested series of 'colonization' models that could be used to study changes in urban landscapes through simulations of housing starts.Within our probabilistic colonization framework, the ecological principle of density-dependence (operating simultaneously on different spatial scales) governs the positioning of new housing units. These simple models afford a great diversity of possible spatial patterns, ranging from tight clustering of houses to urban sprawl to more subtle patterns such as aversion of housing developments from (and aggregation near) different kinds of landscape features. These models can be parameterized from a variety of types of governmental housing data. Ultimately, such a framework could be used to contrast development patterns among cities and identify pertinent operational scales and factors influencing processes associated with urbanization.     

Identification of normal parameters for ultrasonographic examination of the equine large colon and cecum

Six healthy horses were examined by using transabdominal ultrasonography, as described (1-3), to evaluate activity and size of the large colon and cecum at various locations. Using size and number of sacculations, activity patterns and contractile frequency; significant differences that would allow ultrasonographic identification of dorsal versus ventral colons, if they were displaced, were not found. The cecum had significantly greater activity than the colon, and a trend was seen towards smaller sacculations in the cecum than in the large colon.     

IMAGING DIAGNOSIS—USE OF RADIOGRAPHY AND COMPUTED TOMOGRAPHY IN THE DIAGNOSIS OF A MINERALIZED YOLK SAC IN A BROWN KIWI (APTERYX MANTELLI)

A 12‐day‐old Brown Kiwi (Apteryx mantelli) was presented with anorexia, torticollis, head‐tilt, and coelomic distension. Radiographs showed an ill‐defined, fat‐opaque, coelomic mass displacing viscera craniodorsally. Curvilinear mineral opacities were superimposed over the ventral aspect of the mass. Computed tomography demonstrated the presence of mineral within the periphery of a fat attenuating mass consistent with a retained yolk sac. A deutectomy (yolk sac excision) was performed. Histopathology of the excised tissue confirmed the diagnosis of a retained yolk sac with multifocal mineralization.