Rainfall influence upon nutrient inputs to Caribbean coastal systems Tim Carruthers
Outline Thalassia as an indicator for the Caribbean Use of δ 15 N Nutrient sources to a dry Caribbean Lagoon, Yucatan Mexico Nutrient sources to a wet Caribbean Lagoon, Bocas del Toro, Panama Comparison and conclusions
Thalassia testudinum grows in bay, lagoon and reef habitats Thalassia grows near rivermouths in fine mud Thalassia grows in high light Thalassia grows amongst Porites reef in very coarse carbonate sediment maximum depth limit of Thalassia is ca 14% SI
Global distribution of Thalassia T. hemprichii T. testudinum Courtesy Michelle Waycott
Thalassia testudinum (Caribbean) genetically distinct from Thalassia hemprichii (Indo Pacific) Courtesy Michelle Waycott
Thalassia has long distance (2700 km) vegetative dispersal Photo: Bill Dennison Thalassia testudinum Bermuda Thalassia testudinum San Blas, Panama A single genetic individual was collected in both San Blas (Panama) and Bermuda Courtesy Michelle Waycott
Thalassia is relatively long lived with slow turnover therefore a good integrator Courtesy: Bill Dennison
Thalassia testudinum is an ideal sentinel species for the Caribbean Wide dispersal suggests Caribbean is one potentially interbreeding population Within systems, T. testudinum grows from river mouth to reef T. testudinum is a relatively long lived, slow turnover species providing an integrated sample in time T. testudinum is abundant
Method for analysis of δ 15 N Collect sample Dry and grind Analyse on Mass spectrometer ( At%15N At%15N ) sample standard At%14N At%14N δ 15 N (%o) = x 1000 At%15N standard At%14N
Unenriched N source 15 N 0.4% 14 N 99.6% Atmosphere (N 2 ) Rain (630 µg L -1 N) Fixed by Cyanobacteria etc Metabolized N source 15 N 0.4% 14 N 99.6% Within plant/algae/phytoplankton Consumption 15 N 0.4% 14 N 99.6% Digestion & excretion 15 N 0.4% 14 N 99.6% Eg marine δ 15 N= 0 15 N 0.405% 14 N 99.595% Eg marine δ 15 N= 12.5
Nichupte and Puerto Morelos Lagoons are in the north east Caribbean Yucatan peninsula (Mexico) Nichupte and Puerto Morelos Lagoons Photo: NASA
Nichupte and Puerto Morelos Lagoons have groundwater inflow Sink holes Cenotes are common throughout the Yucatan Intense hotel development has occurred and is expanding
Intense and rapid hotel development has occurred in past two decades http://www.cancunsmart.com/
North west Caribbean has 0.8-1.2m annual rainfall with no clear wet and dry Total Monthly (mm) Mean annual rainfall 815-1269 mm Data from Brigit van Tussenbroek
T. testudinum has higher %N in Nichupte Lagoon than in Puerto Morelos Lagoon %C %N %P C:N:P 33.5 2.93 a 0.17 541:42:1 34.4 2.50 ab 0.13 794:50:1 35.6 2.11 bc 0.18 528:26:1 35.2 1.80 c 0.13 740:32:1 p= 0.28 <0.01 0.04 Nichupte Lagoon north Nichupte Lagoon south Puerto Morelos springs Puerto Morelos Lagoon Flushing in Nichupte north is 1.9 yrs Two narrow openings to Nichupte Lagoons
T. testudinum %N in Nichupte Lagoon has increased in last 10 yrs 1991 (mean se ) 2002 (mean se ) %C 36.9 1.16 34.8 0.12 %N 2.04 0.14 2.77 0.19 %P 0.14 0.01 0.12 0.02 C:N:P 680:32:1 749:51:1 C:N 21:1 15:1
Sewage is the source of increasing nitrogen in Nichupte Lagoon %N δ 15 N 33.5 2.93 a a 0.17 9.06 a 541:42:1 34.4 2.50 ab ab 0.13 5.49 ab 794:50:1 35.6 2.11 bc bc 1.90 0.18 528:26:1 35.2 1.80 c c 0.13 1.69 c 740:32:1 p= <0.1 <0.1 Nichupte Lagoon north Nichupte Lagoon south Puerto Morelos springs Puerto Morelos Lagoon
During rain events, T. testudinum near submarine springs has increased %P Nutrient source Increased %P in seagrass tissue implies that either phosphorus or iron is entering Puerto Morelos Reef Lagoon through submarine springs Location season %C %N %P C:N:P n Submarine springs dry 35.6 2.11 0.18 528:26:1 4 Submarine springs rain 39.5 1.85 0.38 275:11:1 3 Lagoon dry 35.3 1.80 0.13 740:32:1 6 Lagoon rain 36.8 1.91 0.14 698:31:1 20 Fe Fe
Nutrient inputs to the west Yucatan Peninsula Fe Fe
Bocas del Toro is in the south west Caribbean Photo: NASA Panama Bocas del Toro
South west Caribbean has 3-6m annual rain with two mini dry seasons Monthly Total Bocas del Toro rainfall (mm) Yucatan rainfall Lower rainfall in Feb/March & Sept/Oct extended dry 2003 Mean annual rainfall 2000-4000 (-6000) mm Data provided by Karl Kauffman
Bocas del Toro has high sediment and nutrient watershed inputs Land clearing for wood Sewage inputs Slumping and hillslope erosion Riverbank erosion, banana plantations
T. testudinum %P high throughout Bocas archipelago, highest in the north Bay 0.26% ±0.01 Reef 0.27% ±0.02 Global : median 0.18% Duarte 1990 0.20% ±0.01 Florida Bay: median 0.11% Fourqurean and Zieman 2002 Lagoon Thalassia testudinum leaf %P
T. testudinum %N high throughout Bocas del Toro archipelago Bay 2.46% ±0.08 Reef 2.46% ±0.14 2.38% ±0.13 Global : median 1.8% Duarte 1990 Florida Bay: median 1.76% Fourqurean and Zieman 2002 Lagoon Thalassia testudinum leaf %N
Thalassia testudinum tissue nutrients Global Florida Seagrass Bay median median Bay Lagoon Reef C:N 20:1 24:1 15:1 15:1 16:1 C:P 435:1 874:1 312:1 364:1 338:1 N:P 22:1 36:1 20:1 24:1 21:1
High nutrient inputs from watershed throughout Bocas del Toro archipelago
Some Lagoons in both Yucatan and Bocas del Toro show nutrient status which is globally high. %N %P C:N:P Sewage (Nichupte) 2.93 0.17 541:42:1 Pristine (PM Lagoon) 1.8 0.13 740:32:1 Bocas 2.40 0.24 350:22:1 Global 1.80 0.18 435:22:1 Florida Bay 1.76 0.11 847:36:1
Conclusions Thalassia is an effective bio-indicator for the Caribbean Use of δ 15 N clarified anthropogenic influences to both high and low rainfall Caribbean systems A dry Caribbean Lagoon, Yucatan shows high sewage nitrogen inputs and high phosphorus inputs from submarine vents A wet Caribbean Lagoon, Bocas del Toro shows high total nitrogen and phosphorus inputs from watershed sources
Recommend watershed management in Bocas del Toro to reduce erosion and fertilizer inputs. Recognition of the extent of impact of riverine inputs is required. Recommendations Thalassia testudinum is a sentinel species, recommend a Caribbean wide database and to assess more locations. Recommend both broad scale and local assessments of δ 15 N to aid in determining nitrogen sources. Recommend management of west Yukatan hotel development, specifically sewage treatment.
Acknowledgements Yucatan: Brigit van Tussenbroek Bill Dennison field Kor Jent, Daniel Flores, Fransisco Renteria UNAM Panama: Penny Barnes Jim Fourqurean field Gabriel Jacome, Victoria Collins, Maricella Salazar, Willy Pomares, Arcardio Castillo, David Kline, Jane Thomas FIU
For more information: IAN (Integration Application Network) www.ian.umces.edu