Biogeochemical impacts of storm runoff on water quality in Southern Kaneohe Bay, Hawai'i

xv, 196 leavesFluvial impacts on water quality and ecosystem structure were evaluated in southern Kaneohe Bay, Oahu, Hawaii. Fluvial inputs occurred as small, steady baseflow interrupted by intense pulses of storm runoff. Baseflow impacted only restricted areas around stream mouths, but the five storm events sampled during this study produced transient runoff plumes of much greater spatial extent. Nutrient loading via runoff generally led to an increase of the phytoplankton biomass and gross productivity in southern Kaneohe Bay, but the rapid depletion of nutrients resulted in a fast decline of the algal population for all storm events considered in this study. Because of variability in export and mixing rates of runoff nutrients, the magnitude of the phytoplankton response was not proportional to nutrient loading. Under baseline conditions, water-column productivity in southern Kaneohe Bay is normally nitrogen-limited. However, following storm events, the high dissolved inorganic nitrogen to dissolved inorganic phosphorus (DIN:DIP) of runoff nutrients drive South Bay waters towards phosphorus-limitation. A depletion of phosphate (PO43-) relative to nitrate (NO3-) in surface waters was observed following all storm events. Due to high flushing rates, recovery times of bay waters from storm perturbations ranged from three to eight days and appeared to be correlated with tidal range. Storm inputs can thus have significant impacts on the water column ecosystem and biogeochemistry in southern Kaneohe Bay, but the perturbations are only transient events

Characterizing Vessel Traffic Using the AIS: A Case Study in Florida\u27s Largest Estuary

Tampa Bay, FL, is a large, ecologically rich estuary that hosts one of the largest commercial ports in Florida. Automatic identification system (AIS) records from 2015 to 2017 were used to determine the number, size, speed, type, and transits of vessels in Tampa Bay. The AIS vessel types were grouped into 10 general classes based on function. The cargo and tanker classes had the highest number of unique vessels transiting the estuary. The tug class had the highest number of individual transits, followed by cargo class. The most common vessel lengths were 165–200 m. Typical drafts were 9–11 m, and ship speeds were almost all/s. Froude numbers calculated from these data indicated that ships were generally underway in displacement mode. Overall,10 m/s. These were identified as smaller passenger and recreational vessels operating in planing mode. The AIS navigational status and speed were often inconsistent, therefore, the combination of speed and duration was used to define individual transits. The average tidal dependency (TD) parameter for all vessels transiting into the bay was −0.02, and 0.10 for combined cargo and tanker vessels. Proper evaluation of the TD required inclusion of the phase lag between the entrance position and the tide gauge

Ship Wakes and their Potential Shoreline Impact in Tampa Bay

Ship wakes generated by vessels moving through ecologically sensitive areas, or near poorly-protected infrastructure, can negatively impact these systems. This is especially true in regions hosting large seaports. Ship wakes in Tampa Bay, Florida, were calculated during two time periods using vessel movement data reported through the Automatic Identification System (AIS). The first period was for the years 2015–2017 using data from a government database. The second was during part of 2018 obtained by local monitoring. Only vessels operating at low Froude numbers were examined. Wake heights were estimated from each AIS record using an empirical equation and partitioned by functional vessel class. The largest estimated wakes were produced by the Passenger class. Cargo class vessels had the largest number of ships estimated to produce high wakes. Egmont Key, a long-eroding barrier island at the mouth of the Bay, was potentially subjected to the highest number of ship wakes and the highest cumulative wake energy. Differences in vessel representation in the two sets of AIS data yielded different distributions of wake energy by vessel class. Some strategies for managing wake energy are discussed

Wakes from Large Vessels and the Risk to the Shoreline Environment in Tampa Bay

The shoreline around Tampa Bay, Florida contains large areas of productive habitat, hosting some of the highest concentrations of wading birds in the US. The bay also contains one of the busiest seaports in the country. Thousands of transits by large vessels such as tankers, cargo ships, and cruise liners are recorded every year through the network of shipping channels within the bay. Their wakes potentially threaten critical shoreline habitat as well as increased erosion around infrastructure and property. Vessel wake heights for the bay were estimated from records of vessel length, draught, and speed extracted from the historical Automatic Identification System (AIS) data. Errors in these data such as unrealistic draught and speed were removed from the analysis. This initial study was limited to the year 2015 and vessel lengths greater than 30 m. Over 560 of these vessels, composed of 26 unique vessel types, passed through Tampa Bay for a total of ~6000 transits. These ships range in size from 30-300 m in length with maximum draughts around 15 m. Ship wake heights were computed using the empirical relation developed for displacement vessels by Kriebel and Seelig (2005) based on the Froude number. Almost all the estimated wake heights were \u3c ;0.6m. About 15% of the AIS reports for ships underway were found to be subcritical, generating no significant wake. Estimated wake heights above 0.5 m were rare, found in ~0.02% of the vessel reports. Some of the high estimates may be due to semiplaning vessels violating the assumptions of the method, yielding unrealistic results. Reducing the block coefficient of vessels moving above their hull speed largely eliminated estimated wake heights \u3e 0.5m